refactor: extract OpenTelemetryServiceFieldsConfig mixin

[lesnik512]

Summary

opentelemetry_service_name and opentelemetry_namespace were declared identically on both OpentelemetryConfig and PyroscopeConfig. In the four framework configs (Free, FastAPI, Litestar, FastStream) that inherit from both parents, Python's MRO happened to pick one declaration; the fact that defaults matched is what kept behavior consistent. Without the mixin, drifting defaults on one side would silently misbehave on the framework configs.

Extract OpenTelemetryServiceFieldsConfig(BaseConfig) — a tiny mixin declaring just those two fields. Both OpentelemetryConfig and PyroscopeConfig now inherit from it (no longer from BaseConfig directly). The duplicate declarations are removed.

PyroscopeConfig's standalone use case (without OpentelemetryConfig in the MRO) is preserved — exercised by test_pyroscope_standalone_config_accepts_otel_fields.

Closes DES-2 from an internal audit.

Test plan

• just test -- tests/instruments/test_opentelemetry_instrument.py tests/instruments/test_pyroscope_instrument.py -v — pass.
• just test — full suite 89/89.
• just lint — clean.
• Reviewer: confirm the new dependency direction (pyroscope_instrument → opentelemetry_instrument) is acceptable. Code review confirmed: no circular import — opentelemetry_instrument imports the pyroscope package, not pyroscope_instrument.

Notes for reviewer

The MRO for FreeBootstrapperConfig(LoggingConfig, OpentelemetryConfig, PyroscopeConfig, SentryConfig) resolves as:
FreeBootstrapperConfig → LoggingConfig → OpentelemetryConfig → PyroscopeConfig → OpenTelemetryServiceFieldsConfig → SentryConfig → BaseConfig → object

OpenTelemetryServiceFieldsConfig appears exactly once via C3 linearization — both children share the same ancestor.

Cosmetic future-work note: OpentelemetryConfig (lowercase t) sits next to the new OpenTelemetryServiceFieldsConfig (uppercase T) — same module, different casing. Worth a rename + deprecation alias in a follow-up PR. Out of scope here.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
..._bootstrap/instruments/opentelemetry_instrument.py	100.00% <100.00%> (ø)
lite_bootstrap/instruments/pyroscope_instrument.py	100.00% <100.00%> (ø)

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