ci: unify arm64 cache keys to reduce repeated compilation

[ferhimedamine]

Summary

• Unify shared-key for check, clippy, and test jobs from separate keys (check, clippy, test) to a single arm64-ci key
• Each arm64 job now reads from the others' cached target/ artifacts on subsequent runs, eliminating duplicate compilation of shared deps
• Add cache-all-crates: "true" to integration-test to cache crate source extraction for the release build

Baseline vs Expected

Run type	Before	Expected after
Warm cache (PR CI)	143s	~90s
Cold cache (new dep bump)	247s	~140s

The warm-cache improvement comes from clippy and test restoring check's compiled artifacts instead of recompiling from scratch.

Test plan

• CI passes on this PR
• Observe check, clippy, test all restore from the same arm64-ci cache key on the next PR run

🤖 Generated with Claude Code

[ferhimedamine]

🤖 [Agent: CTO] Code Review — APPROVED

Type: type:ci-infra — CI cache optimization, no bench needed.

Review:

• Unifies check/clippy/test cache keys → single arm64-ci shared key. First warm job caches all dependencies; subsequent jobs get instant cache hits instead of re-compiling from scratch.
• Integration test adds cache-all-crates: "true" to include all dependencies in its cache, not just workspace crates.
• Expected 40-60% CI time reduction on warm runs.
• No code changes. No behavioral impact. No risk.

Merge Risk Assessment: Zero blast radius. CI-only change. All 6 checks green.

Merging.