accelerate CI via cargo binstall

[plebhash]

accelerate CI via cargo-binstall

instead of compiling cargo-nextest and cargo-semver-checks on every run, we install pre-built binaries via cargo-binstall.

additional hardening:

• disable quick-install to only use upstream release artifacts (instead of third-party quick-install artifacts)
• pass GITHUB_TOKEN to cargo-binstall to avoid unauthenticated GitHub API rate-limit fallback
• use --locked for deterministic fallback behavior if source install is ever needed

estimated impact (latest successful PR run vs median of 5 recent comparable successful PR runs on the same workflows/jobs):

• ci (ubuntu-latest):
  • tool install: ~2m34s -> ~3s (~98% reduction)
  • total job: ~32m18s -> ~28m41s (~3m37s faster, ~11%)
• ci (macos-latest):
  • tool install: ~2m38s -> ~5s (~97% reduction)
  • total job: ~31m57s -> ~30m04s (~1m53s faster, ~6%)
• semver-check:
  • tool install: ~5m09s -> ~4s (~99% reduction)
  • total job: ~15m04s -> ~9m44s (~5m20s faster, ~35%)

critical-path wall clock also improves (~32m18s -> ~30m04s, ~2m14s), while matrix jobs still run in parallel.

[Shourya742]

ACK.

[Shourya742]

@plebhash can you rebase this? And can you also squash the commits (kinda similar changes)