Fix docs.rs build failure for metrique crate

Summary

The docs.rs build for metrique 0.1.21 fails because the global-state example has doc-scrape-examples = true and uses metrique_util::State, but metrique-util was only a dev-dependency. On docs.rs, dev-dependencies are stripped, so example scraping fails with unresolved import metrique_util.

Two changes:

1. check-docsrs.sh: the script was not catching this class of failure. When the packaged docs-rs build failed, it silently fell back to a workspace build where dev-deps are available, masking the error. The fix removes the fallback when the packaged build itself fails (the fallback is preserved only when cargo package fails, e.g. for unpublished crates). It also restores doc-scrape-examples = true flags that cargo package may strip from the packaged Cargo.toml, so the packaged build faithfully reproduces docs.rs behavior.

2. metrique/Cargo.toml: adds metrique-util as an optional dependency behind a new util feature (which enables metrique-util/state). The global-state example is gated on required-features = ["emf", "service-metrics", "util"]. Since docs.rs builds with --all-features, the feature is enabled and the example compiles during doc scraping.

Testing

• Verified check-docsrs.sh metrique reproduces the exact docs.rs error before the Cargo.toml fix (E0432: unresolved import metrique_util).
• Verified check-docsrs.sh metrique passes after the Cargo.toml fix.
• cargo check -p metrique --all-features passes.

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