refactor(telemetry): align metrics/pricing init with tracing pattern

[ajbozarth]

Pull Request

Issue

Fixes #

Description

Brings mellea.telemetry.metrics and mellea.telemetry.pricing onto the same module-init pattern that mellea.telemetry.tracing adopted in #1181. Eliminates importlib.reload(mellea.telemetry.*) from every telemetry test (~40 sites) and consolidates the three drifted copies of _reset_tracing_state() that PR #1181 left behind.

No public API change. No production behavior change. Test side absorbed nearly all of the diff.

Why: after #1181, tracing.py was the only telemetry pillar with its init logic in a recallable _setup_tracing() function. metrics.py and pricing.py still captured env vars into module-level constants at the top of the module, which forced every test that toggled an env var to importlib.reload(mellea.telemetry.metrics) to re-execute the module body. Each reload re-runs imports and side effects — slow, noisy, and fragile.

Source-side changes:

• metrics.py — Module-level env-read constants removed. The seven private _METRICS_* / _OTLP_METRICS_ENDPOINT / _SERVICE_NAME / _EXPORT_INTERVAL_MILLIS constants no longer exist; env-var reads live inside _setup_meter_provider(), matching tracing.py. The hot-path gate in every record_* function checks _meter is None directly (semantically equivalent to the old _METRICS_ENABLED check). Also fixes a parallel of the tracing-side regression caught in fix: reload module for telemetry testing so all tests can run #805: _meter is now bound off the freshly built provider rather than via OTel's global metrics.get_meter(), since set_meter_provider() is one-shot per process and the global meter would otherwise fall back to the original (now shutdown) provider after a reset.
• pricing.py — Init logic wrapped in _setup_pricing(). Same shape as the others; no production behavior change.

Minor cleanup: the redundant if is_tracing_enabled(): guard at the module-load _setup_tracing() call site is dropped (the function early-returns on its own), and is_metrics_enabled() / is_tracing_enabled() now cache their result like is_pricing_enabled() already does.

Test-side changes:

• New test/telemetry/conftest.py with shared reset_metrics_state(), reset_tracing_state(), reset_logging_state(), reset_pricing_state() helpers replacing all importlib.reload calls. New regression test test_meter_remains_functional_after_repeated_resets exercises _setup_metrics() across multiple reset cycles and asserts recordings still land in the active reader.
• Tracing test reset DRY-up: three drifted per-file copies of _reset_tracing_state() consolidated. test_tracing.py and test_tracing_backend.py previously omitted the _tracer_provider.shutdown() call that test_tracing_plugins.py had — the consolidated helper does the shutdown for all three. Strictly safer cleanup; no perceptible slowdown (idle BatchSpanProcessor workers join in microseconds).
• Test mocking layer change for _LITELLM_AVAILABLE and _OTEL_AVAILABLE: tests no longer manipulate sys.modules to fake import failure. They now use monkeypatch.setattr(...) directly on the module attribute. Same code paths exercised; module-load-time try: import ... blocks are no longer reverified per-test.
• Test assertions in test_metrics.py shifted from cached env captures (_METRICS_CONSOLE is True, _OTLP_METRICS_ENDPOINT == "...", etc.) to behavior on the constructed MeterProvider (resource attributes, attached metric readers, mock-patched exporter call args). Strictly stronger — proves env values were both read and applied.
• test/telemetry/__init__.py added so from test.telemetry.conftest import ... resolves under mypy. Same pattern test/plugins/__init__.py already uses.

What didn't change:

• Public API: is_metrics_enabled(), is_tracing_enabled(), is_pricing_enabled(), get_otlp_log_handler(), all record_* and create_* functions — same signatures, same semantics.
• Production behavior: no env var renames, no breaking changes, no warning text changes.
• Documentation: no doc updates required.
• Plugin registration: _plugins_registered semantics preserved (process-global, intentionally not reset by tests).

Testing

• Tests added to the respective file if code was changed
• New code has 100% coverage if code was added
• Ensure existing tests and github automation passes (a maintainer will kick off the github automation when the rest of the PR is populated)

$ uv run pytest test/telemetry/ -m "not qualitative"
211 passed, 17 deselected

2 e2e tests in test_metrics_backend.py::test_huggingface_token_metrics_integration fail on local — pre-existing huggingface.py:1119 torch tensor-indexing issue, unrelated to this PR. Not seen in -m "not e2e".
Opened #1253

Attribution

• AI coding assistants used

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