Add build_script_env_files crate annotation

[finn-ball]

Summary

Add build_script_env_files support to crate.annotation, allowing environment files to be passed to generated cargo_build_script targets.

The change:

• Exposes build_script_env_files through bzlmod and legacy crate annotations.
• Propagates the annotation through crate-universe configuration and build-script context.
• Renders the attribute on generated cargo_build_script rules.
• Supports unconditional and platform-selected values.
• Updates the configuration digest.
• Adds tests for annotation propagation and BUILD-file rendering.

Testing

• bazel test //crate_universe:unit_test