ci: remove shared Actions caches from release-sensitive workflows

[prd-carapulse]

Summary

• Remove setup-node yarn caching from the shared install action used by the manual npm release workflow.
• Stop restoring/saving Forge compilation caches in the pull_request Foundry workflow.
• Delete the now-unused install-cache composite action.
• Pin setup-node and foundry-toolchain in the shared install action to satisfy the repository Actions policy.

Request Context

• Initiator: tarik (Slack display name; GitHub login unresolved)
• Initial Slack thread: Slack channel C0B3Z936HR6, thread_ts 1778551077.528289
• Rationale: Requested to prevent GitHub Actions cache poisoning pattern.

Verification

• git diff --check
• CI failure follow-up: pinned external actions used by the shared install composite action.
• Text check: no .github workflow/action file still references actions/cache, cache: yarn, or install-cache.

Notes

• No GitHub assignee was added because I only have the Slack display name tarik, and I do not want to guess a GitHub login.
• This PR only changes GitHub Actions cache usage; it does not change product/runtime code.

[prd-carapulse]

Resolved merge conflicts in f09de2e.

Resolution:

• Kept PR ci: remove shared Actions caches from release-sensitive workflows #90 cache removal: .github/actions/install-cache/action.yml stays deleted.
• Updated Foundry jobs to use ./.github/actions/install and removed forge cache save/restore.
• Preserved main's pnpm migration and removed the malformed nested Enable pnpm steps from affected workflows; pnpm setup now lives in the shared install action.

Verification:

• Parsed all .github/**/*.yml / .yaml with PyYAML.
• pnpm install --frozen-lockfile --ignore-scripts
• pnpm run lint
• pnpm run build:forge --force --sizes
• pnpm run build:hardhat --force
• Remote checks on f09de2e: lint, Foundry compilation/tests, Hardhat gas tests, and Aikido are green. Certora still finishing.

PR is now MERGEABLE; current blocker is review re-approval after head update.