ci: switch PR, dry-run, and release validation to the sharded topology

Flip shard_suites on for all three callers of the reusable test
workflow. This commit is deliberately the only topology change:
reverting it alone restores the previous single-job-per-leg CI shape
while keeping the (inert without it) sharding machinery and the
cache-warm pipeline.

Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>

Author: DeusData

.github/workflows/dry-run.yml

@@ -51,6 +51,7 @@ jobs:
     with:
       skip_perf: true
       broad_platforms: true
+      shard_suites: true
 
   # ── Build all platforms ────────────────────────────────────────
   build:

.github/workflows/pr.yml

@@ -35,6 +35,10 @@ jobs:
       # Perf assertions are timing-sensitive on shared runners; they stay in
       # dry runs and releases where a flaky red does not block a merge.
       skip_perf: true
+      # Iteration speed: split each C-suite leg across parallel shard jobs
+      # (ubuntu x3, windows x2; coverage re-proven every run by the
+      # shard-completeness job). Dry runs and releases shard identically.
+      shard_suites: true
 
   # ── Which files changed? Gate the (heavier) build+smoke on product code so
   #    docs / CI / test-only PRs stay fast. ──

.github/workflows/release.yml

@@ -52,6 +52,7 @@ jobs:
     with:
       skip_perf: ${{ inputs.skip_perf }}
       broad_platforms: true
+      shard_suites: true
 
   # ── 3. Build all platforms ──────────────────────────────────────
   build: