chore: consolidate dependency updates

[avifenesh]

Summary

• refresh the pinned Rust cache action
• update the GPUI lockfile revision and rmcp 3.1.3
• satisfy the Rust 1.98 chunks_exact_to_as_chunks lint exposed by all four bot PRs

Supersedes #73, #74, #75, and #76.

Validation

• cargo fmt --check
• cargo clippy --all-targets -- -D warnings
• cargo test --all-targets - 180 passed
• git diff --check

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[revuto-review]

This is an auto review done by revuto.

---

Revuto completed the review and found no evidence-backed concerns.

[avifenesh]

Weekly maintenance recheck: local fmt, Clippy, and all 180 tests pass; every CI/security check and the exact-head Revuto review are green, with zero unresolved review threads. This PR is ready to merge but branch protection still requires one qualifying human approval. The covering PR must merge before superseded Dependabot PRs #73-#76 are closed.

[avifenesh]

Final authenticated sweep recheck: head 84bdb80 is unchanged; all CI, CodeQL, agnix, and exact-head Revuto checks pass with zero unresolved threads. Branch protection still requires one qualifying human approval, so this cover cannot merge from the author account. Dependabot PRs #73-#76 remain open until this cover merges.