refactor(token_usage): move functions to TokenUsageProvider directly

[alexsnaps]

See #284

But, tl;dr, there is no need to have TokenUsageProvider be Clone or Copy (and copy it all over the place). This closes the door to eventually add state seamlessly in the future. Finally, both the methods where methods all along, so made them that, using &self

[praxis-bot-app]

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[praxis-bot]

Review: refactor(token_usage): move functions to TokenUsageProvider directly

Clean mechanical refactoring. Reviewed all four changed files in full plus the unchanged consumer filters/src/token_count/tests.rs to verify no implicit Copy/Clone dependencies were missed.

What was checked

• Correctness: match *self correctly dereferences &Self for enum pattern matching. All callers updated from free-function syntax to method syntax. The pub(super) visibility on parse_anthropic_event / parse_bedrock_event is the minimum needed for the impl TokenUsageProvider block in the parent module.
• Caller completeness: Searched all code references to extract_token_usage, extract_streaming_tokens, and TokenUsageProvider across the repo. Every code-level caller is covered by the diff. The only remaining references to the old free functions are in docs/proposals/ design documents (not compiled).
• Implicit Copy consumers: filters/src/token_count/tests.rs (not in the diff) passes TokenUsageProvider by value into make_filter() and the run_*_extraction helpers. These are moves, not copies, so they compile without Copy. Confirmed by all 17 CI checks passing.
• API surface: Removing Clone, Copy, and the two public free functions is a breaking change, but appropriate for a 0.1.0 crate where all consumers are workspace-internal.
• Test coverage: The test changes are purely syntactic (free function calls to method calls). No tests were added or removed, which is correct since no behavior changed.
• Convention compliance: File ordering, section separators, doc comments, visibility, and import grouping all conform to workspace conventions.

Severity table

Severity	Count
Critical	0
Large	0
Medium	0

No findings. The refactoring is correct, complete, and consistent.