fix(ci): deduplicate pnpm install in run_single_test and refine turbo compile inputs

[quirogas]

In CI, .github/actions/pnpm-lockfile-check already runs pnpm install once at the start of every job for the whole monorepo. However, ci/run_single_test.sh was still running pnpm install again inside every package directory it tested. Because the repo is now a single pnpm workspace, each of those calls re-checks the entire monorepo, which slows down test shards and causes Windows runs to time out on large PRs.

This PR updates ci/run_single_test.sh to skip pnpm install when node_modules is already installed at the root, and cleans up a few related test settings so unit tests run reliably.

What changed

• ci/run_single_test.sh: Only run pnpm install --frozen-lockfile --ignore-scripts if node_modules/.pnpm is missing at the workspace root (for local runs). --ignore-scripts is used because most packages in the repo define "prepare": "npm run compile", which would otherwise compile the entire monorepo during install. Also lower --max_old_space_size from 6 GB to 2 GB on Windows so parallel Mocha workers don't run out of memory.
• .npmrc: Set enable-pre-post-scripts=true so package pretest and postcompile hooks (like building pprof in cloud-profiler or copying protos in nodejs-proto-files) run automatically during pnpm compile and pnpm test.
• turbo.json: Remove package.json from compile.inputs so editing package.json scripts or versions doesn't invalidate the TypeScript build cache for every package.
• handwritten/firestore/.mocharc.js: Add "exit": true (matching the root .mocharc.cjs) so Mocha exits after tests finish instead of hanging on open gRPC connections.

[gemini-code-assist]

Code Review

This pull request optimizes the CI test execution script by adjusting Node.js memory limits based on the operating system, optimizing dependency installation, and conditionally compiling packages using Turbo. It also updates the Mocha configuration for Firestore to force exit, adjusts Turbo compilation flags in package.json, and removes package.json from Turbo's input files. A critical issue was identified in ci/run_single_test.sh where an undefined variable 'd' is used, which should be replaced with '.' to correctly resolve the relative path.