feat: Avoid touching wrapper files when content is unchanged

[breezewish]

Fix #239

This PR simply adds a check for most wrapper writes: Try to read first, then write if the content should be changed.

Verified that ccache works across different builds for rust-rocksdb with the default config:

ccache --set-config=compiler_check=mtime # Default

[2024-04-16T13:44:19.059926 67945] Succeeded getting cached result
[2024-04-16T13:44:19.059943 67945] Result: direct_cache_hit
[2024-04-16T13:44:19.059944 67945] Result: local_storage_hit
[2024-04-16T13:44:19.059945 67945] Result: local_storage_read_hit
[2024-04-16T13:44:19.059946 67945] Result: local_storage_read_hit

[messense]

LGTM, thanks!

[messense]

CI failures with zig master or Rust nightly is fine, we'll deal with it when new zig/Rust release is out.