ci: Remove path-based workflow scheduling (#13332)
## Why
CI reimplemented repository ownership with handwritten path filters even
though Cargo crates and native package dependencies now live in Turbo's
graph. The duplicate scheduler was large, fragile, and easy to drift
from actual task inputs.
## What
Run the normal PR matrices consistently, let Turbo scope/cache task
work, and retain the existing release-PR validation and skip behavior
unchanged. Rust test inputs now cover root-level configuration,
integration fixtures, and `version.txt`.
## How
- Consolidates Rust tests into one three-platform matrix.
- Routes lockfile integration through its graph dependency on
`turbo#build`.
- Removes path classifiers from Test, JS Package Tests, and Lint
workflows.
- Uses OIDC Remote Cache for pushes and same-repository PRs; fork PRs
remain local-only.
- Isolates nested Turbo integration tests from the outer sccache wrapper
environment.
- Leaves examples push-only and leaves
`.github/workflows/turborepo-release.yml` untouched.
Validation:
- `actionlint` passes for all changed workflows; only known custom
runner labels were ignored.
- `oxfmt --check` and `cargo fmt --check` pass.
- Rust task dry-run includes `version.txt`, nextest/Insta configuration,
and integration fixtures.
- Full lockfile suite: 258 passed, 1 expected failure, 0 unexpected
failures.
- Trusted PR run authenticated successfully and reported 687-688
incremental-cache hits per Unix platform.
- Both nested Cargo integration tests pass with an intentionally invalid
ambient `RUSTC_WRAPPER`.
- Security and CI reviews confirmed the same-repository/fork trust
boundary.
Expected tradeoff: fork PRs may perform more uncached Rust work.
