fix: don't generate AnyEvent for eventless schemas

[johanpel]

Description

If a schema declares no events, don't generate an AnyEvent.

[coderabbitai]

📝 Walkthrough

Walkthrough

generate_any_event now returns an empty token stream for schemas without entities, avoiding event-derive processing and enum generation. A unit test covers this behavior, and Options::any_event documentation describes the no-event case.

Changes

AnyEvent generation

Layer / File(s)	Summary
Skip empty AnyEvent output crates/instrumentation-build/src/any_event.rs, crates/instrumentation-build/src/lib.rs	Variant collection now precedes derive processing, empty variants return no tokens, a regression test verifies the result, and the option documentation describes this behavior.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• rapidsai/quent#400: Introduced the AnyEvent generator behavior refined by this change.

Suggested reviewers: dhruv9vats, mbrobbel

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is concise and accurately states the main change to skip AnyEvent generation for eventless schemas.
Description check	✅ Passed	The description explains the change, but it omits related issues, testing, and screenshots sections from the template.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[johanpel]

/merge