fix(tracing-limit): group info!(message = "foo") and info!("foo") in same bucket

[WaterWhisperer]

Summary

Previously, these two equivalent log formats were treated as separate rate limit groups due to different callsite identifiers. Now, rate limiting is based on message content and contextual fields (like component_id) rather than callsite.

Vector configuration

N/A - This is an internal library change to the tracing-limit crate. No Vector configuration is required for testing.

How did you test this PR?

• Added a new test message_field_explicit_vs_implicit_same_bucket that verifies both info!(message = "Hello") and info!("Hello") are grouped under the same rate limit bucket
• All 9 existing tests in the tracing-limit crate pass
• Ran cargo test -p tracing-limit to verify no regressions
• Ran cargo clippy -p tracing-limit with no warnings

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

References

• Closes: bug(tracing_limit): info!(message = "foo") and info!("foo") are not grouped under the same bucket #24054

Notes

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