otel: remove the last workspace crate feature

[bolinfest]

Why

codex-otel still carried disable-default-metrics-exporter, which was the last remaining workspace crate feature.

We are removing workspace crate features because they do not fit our current build model well:

• our Bazel setup does not honor crate features today, which can let feature-gated issues go unnoticed
• they create extra crate build permutations that we want to avoid

For this case, the feature was only being used to keep the built-in Statsig metrics exporter off in test and debug-oriented contexts. This repo already treats debug_assertions as the practical proxy for that class of behavior, so OTEL should follow the same convention instead of keeping a dedicated crate feature alive.

What changed

• removed disable-default-metrics-exporter from codex-rs/otel/Cargo.toml
• removed the codex-otel dev-dependency feature activation from codex-rs/core/Cargo.toml
• changed codex-rs/otel/src/config.rs so the built-in OtelExporter::Statsig default resolves to None when debug_assertions is enabled, with a focused unit test covering that behavior
• removed the final feature exceptions from .github/scripts/verify_cargo_workspace_manifests.py, so workspace crate features are now hard-banned instead of temporarily allowlisted
• expanded the verifier error message to explain the Bazel mismatch and build-permutation cost behind that policy

How tested

• python3 .github/scripts/verify_cargo_workspace_manifests.py
• cargo test -p codex-otel
• cargo test -p codex-core metrics_exporter_defaults_to_statsig_when_missing
• cargo test -p codex-app-server app_server_default_analytics_
• just bazel-lock-check

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve test-time exporter disable outside debug assertions

Switching the Statsig guard to cfg!(debug_assertions) means tests built with optimized profiles (cargo test --release or any profile with debug-assertions = false) will now resolve OtelExporter::Statsig to a real OTLP endpoint instead of None. Before this change, the workspace feature kept test runs from emitting network telemetry regardless of optimization level; with this condition, those test contexts can perform outbound export unexpectedly and become flaky/fail in network-restricted environments.

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[bolinfest]

We don't claim that cargo test --release works in this project.