fix(core): support OTLP protobuf protocol

[iw-an]

Issue for this PR

Closes #33101

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Adds support for OTLP HTTP protobuf export configuration.

Previously observability always used JSON serialization for Effect OTLP logs and the JSON trace exporter. This meant OTEL_EXPORTER_OTLP_PROTOCOL=http/protobuf and the signal-specific protocol env vars were not honored.

This PR reads:

• OTEL_EXPORTER_OTLP_PROTOCOL
• OTEL_EXPORTER_OTLP_TRACES_PROTOCOL
• OTEL_EXPORTER_OTLP_LOGS_PROTOCOL

Logs now use the matching Effect OtlpSerialization layer, and traces now choose the JSON or protobuf OpenTelemetry trace exporter based on the trace protocol. Workspace startup also passes these OTEL protocol env vars through so child workspaces keep the same observability configuration.

Unsupported protocol values fall back to http/json.

How did you verify your code works?

Ran from packages/core:

• bun test test/effect/observability.test.ts
• bun typecheck

Also ran:

• git diff --check

Screenshots / recordings

N/A, not a UI change.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

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Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

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[github-actions]

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