[BUILD] Fix curl header target location, otlp test deps, and visibility

Three mechanical Bazel wiring fixes to make PR open-telemetry#4634 build:

1. Move curl implementation_headers from ext/src/http/client/curl/BUILD
   to ext/BUILD and rename to curl_implementation_headers with full
   paths. Bazel was looking for bare filenames in the wrong package.

2. Add //ext:server_headers dep to exporters/otlp:otlp_http_exporter_test
   which includes opentelemetry/ext/http/server/http_server.h (line 64,
   inside conditional block with two spaces in #  include directive).

3. Add //exporters/otlp:__pkg__ to server_headers visibility list so
   the test dependency (fix open-telemetry#2) doesn't fail visibility checks.

Also:
- Remove stale //exporters/jaeger:__pkg__ from http_client_detail
  visibility (jaeger package no longer exists in this repo).
- Sort hdrs, visibility, and deps lists alphabetically per buildifier.
- Note: //exporters/zipkin needs no changes; it reaches curl headers
  transitively via http_client_curl.

Verified against reviewer's local build: bazel build (1972 actions),
bazel test //ext/... //exporters/... (40/40 pass), buildifier (0 findings).

Author: ParthibanRajasekaran

exporters/otlp/BUILD

@@ -810,6 +810,7 @@ cc_test(
     deps = [
         ":otlp_http_exporter",
         "//api",
+        "//ext:server_headers",
         "//sdk/src/metrics",
         "//test_common/src/http/client/nosend:http_client_nosend",
         "@com_google_googletest//:gtest_main",

ext/BUILD

@@ -9,9 +9,9 @@ package(default_visibility = ["//visibility:public"])
 cc_library(
     name = "headers",
     hdrs = [
+        "include/opentelemetry/ext/http/client/curl/http_client_factory_curl.h",
         "include/opentelemetry/ext/http/client/http_client.h",
         "include/opentelemetry/ext/http/client/http_client_factory.h",
-        "include/opentelemetry/ext/http/client/curl/http_client_factory_curl.h",
         "include/opentelemetry/ext/http/common/url_parser.h",
     ],
     strip_include_prefix = "include",
@@ -20,6 +20,28 @@ cc_library(
     ],
 )
 
+# Internal: curl implementation headers
+# Used by: the curl client itself, its tests, and the w3c test server
+# These are implementation details and are not installed by CMake
+cc_library(
+    name = "curl_implementation_headers",
+    hdrs = [
+        "include/opentelemetry/ext/http/client/curl/http_client_curl.h",
+        "include/opentelemetry/ext/http/client/curl/http_operation_curl.h",
+        "include/opentelemetry/ext/http/client/curl/http_time_util.h",
+    ],
+    strip_include_prefix = "include",
+    visibility = [
+        "//ext/src/http/client/curl:__pkg__",
+        "//ext/test/http:__pkg__",
+        "//ext/test/w3c_tracecontext_http_test_server:__pkg__",
+    ],
+    deps = [
+        ":headers",
+        "@curl",
+    ],
+)
+
 # Internal: Detail headers for factory implementations
 # Used by: exporters/otlp, exporters/elasticsearch, exporters/zipkin
 # Breaking change in v2.0.0: moved from public to internal target
@@ -30,11 +52,10 @@ cc_library(
     ],
     strip_include_prefix = "include",
     visibility = [
-        "//ext/src/http/client/curl:__pkg__",
         "//exporters/elasticsearch:__pkg__",
-        "//exporters/jaeger:__pkg__",
         "//exporters/otlp:__pkg__",
         "//exporters/zipkin:__pkg__",
+        "//ext/src/http/client/curl:__pkg__",
     ],
     deps = [
         ":headers",
@@ -50,16 +71,17 @@ cc_library(
         "include/opentelemetry/ext/http/server/http_server.h",
         "include/opentelemetry/ext/http/server/socket_tools.h",
     ],
+    linkopts = select({
+        "//bazel:windows": ["-DEFAULTLIB:Ws2_32.lib"],
+        "//conditions:default": [],
+    }),
     strip_include_prefix = "include",
     visibility = [
+        "//examples/http:__pkg__",
+        "//exporters/otlp:__pkg__",
         "//ext/test/http:__pkg__",
         "//ext/test/w3c_tracecontext_http_test_server:__pkg__",
-        "//examples/http:__pkg__",
     ],
-    linkopts = select({
-        "//bazel:windows": ["-DEFAULTLIB:Ws2_32.lib"],
-        "//conditions:default": [],
-    }),
     deps = [
         "//api",
     ],

ext/src/http/client/curl/BUILD

@@ -5,33 +5,6 @@ load("@rules_cc//cc:cc_library.bzl", "cc_library")
 
 package(default_visibility = ["//visibility:public"])
 
-# Internal implementation headers for curl HTTP client
-# Used by: curl client implementation, internal tests, w3c test server
-# These are implementation details that should not be depended on by external code
-cc_library(
-    name = "implementation_headers",
-    hdrs = [
-        "http_client_curl.h",
-        "http_operation_curl.h",
-        "http_time_util.h",
-    ],
-    strip_include_prefix = ".",
-    visibility = [
-        ":__pkg__",
-        "//ext/src/http/client/curl:__pkg__",
-        "//ext/test/http:__pkg__",
-        "//ext/test/w3c_tracecontext_http_test_server:__pkg__",
-    ],
-    linkopts = select({
-        "//bazel:windows": ["-DEFAULTLIB:Ws2_32.lib"],
-        "//conditions:default": [],
-    }),
-    deps = [
-        "//ext:headers",
-        "@curl//:curl",
-    ],
-)
-
 cc_library(
     name = "http_client_curl",
     srcs = [
@@ -57,6 +30,7 @@ cc_library(
     linkstatic = True,
     deps = [
         "//api",
+        "//ext:curl_implementation_headers",
         "//ext:headers",
         "//sdk:headers",
         "//sdk/src/common:random",

ext/test/http/BUILD

@@ -24,10 +24,10 @@ cc_test(
     defines = ["ENABLE_OTLP_RETRY_PREVIEW"],
     tags = ["test"],
     deps = [
+        "//ext:curl_implementation_headers",
         "//ext:headers",
         "//ext:server_headers",
         "//ext/src/http/client/curl:http_client_curl",
-        "//ext/src/http/client/curl:implementation_headers",
         "//sdk/src/trace",
         "@com_google_googletest//:gtest_main",
         "@curl",

ext/test/w3c_tracecontext_http_test_server/BUILD

@@ -19,10 +19,10 @@ cc_binary(
     deps = [
         "//api",
         "//exporters/ostream:ostream_span_exporter",
+        "//ext:curl_implementation_headers",
         "//ext:headers",
         "//ext:server_headers",
         "//ext/src/http/client/curl:http_client_curl",
-        "//ext/src/http/client/curl:implementation_headers",
         "//sdk/src/trace",
         "@curl",
         "@github_nlohmann_json//:json",