otel: User-Facing API

[schloerke]

Goal: Provide context managers and decorators for user control over OTel collection.

Tasks

• Create shiny/otel/_decorators.py with:
  • otel_collect(level) - Context manager to temporarily set collection level
  • @otel_collect(level) - Decorator version for functions
  • Support both string and enum levels
• Export public API in shiny/otel/__init__.py:
  • otel_collect
  • CollectLevel
  • should_collect
• Export at top-level in shiny/__init__.py:
  • Add from .otel import otel_collect, CollectLevel
  • Update __all__

Acceptance Criteria

• Users can use with otel_collect("none"): to disable telemetry in a block
• Decorator @otel_collect("reactivity") works on functions
• Environment variable SHINY_OTEL_COLLECT sets default level
• Context manager overrides take precedence over env var
• Can import as from shiny import otel_collect or from shiny.otel import otel_collect
• Nested context managers work correctly

Files to Create

• shiny/otel/_decorators.py

Files to Modify

• shiny/otel/__init__.py
• shiny/__init__.py