## Summary

- Upgrade sccache from 0.10.0 to 0.16.0 on macOS, Linux, and Windows CI
runners.
- Normalize the GitHub workspace with `SCCACHE_BASEDIRS` so identical
builds can reuse cache entries across checkout roots.
- Validate the cached binary version and stop an older server before
replacing it, including on Windows where a running executable cannot be
overwritten.

## Why

The setup scripts configured `SCCACHE_BASEDIR`, which sccache did not
use for cache-key path normalization. Absolute checkout paths therefore
remained part of cache keys and reduced reuse between CI workspaces.
sccache 0.16.0 supports `SCCACHE_BASEDIRS` and includes the Windows
path-normalization fix needed for the Windows runner.

## Validation

- `bash -n script/setup-sccache`
- `git diff --check`
- Upgraded a live local sccache 0.15.0 server to 0.16.0 through the
setup script.
- Compiled identical C sources from two checkout roots and observed one
cache miss followed by one cache hit.
- Confirmed that every release asset referenced by the setup scripts
exists for the supported CI runner targets.

Release Notes:

- N/A