feat!: restructure SDK with multi-targeting, test suites and modern HTTP/logging

[Renancp01]

Summary

• Multi-target net8.0;net10.0 — existing .NET 8 consumers keep working, new ones get .NET 10
• Rename projects/solution to .NET naming convention (Inter.Sdk, Inter.Sdk.UnitTests, Inter.Sdk.IntegrationTests, Inter.Sdk.FunctionalTests)
• Remove orphan netstandard2.0 project (src/, inter-sdk-csharp.csproj) and stop tracking build artifacts (bin/, obj/, .idea/)
• Add Inter.Sdk.UnitTests (29 tests): enums, config, URL building, error parsing, model serialization, logging
• Add Inter.Sdk.IntegrationTests (62 tests): every public client method tested end-to-end against a local WireMock server (no credentials needed, CI-ready), plus an optional sandbox suite gated by INTER_* environment variables
• Migrate HTTP layer from obsolete HttpWebRequest (SYSLIB0014) to pooled HttpClient, preserving public signatures, 429 retry and error parsing behavior
• Pluggable logging via Microsoft.Extensions.Logging: inject any ILogger (Serilog/Loki, OpenTelemetry, console...); request/response bodies log at Debug level; token responses are never logged; default file logger preserves the historical logs/inter-sdk-{Day}.log behavior
• Optional Config.BaseUrl override (tests, proxies)
• English README and NuGet publishing workflow (tag v* → nuget.org, requires NUGET_API_KEY secret)

⚠️ BREAKING CHANGE

Root namespace changed from inter_sdk_library to Inter.Sdk (standard .NET PascalCase naming) and the assembly/package is now Inter.Sdk 2.0.0 instead of inter-sdk-library.

Migration for consumers:

- using inter_sdk_library;
+ using Inter.Sdk;

DLL/package references must point to the new Inter.Sdk name.

Open questions for maintainers

• NuGet package ID strategy: confirm Inter.Sdk availability / reserved prefix on nuget.org and which org account holds the publish key
• Release communication plan for the 2.0.0 breaking change

Test evidence

• dotnet test Inter.Sdk.UnitTests → 29 passed (net8.0 and net10.0)
• dotnet test Inter.Sdk.IntegrationTests → 62 passed + 1 skipped sandbox (net8.0 and net10.0)
• dotnet pack Inter.Sdk -c Release → Inter.Sdk.2.0.0.nupkg builds cleanly