[upstream-sync] feat(telemetry): add optional application label via env var (upstream #1992)

[github-actions]

Upstream Change Summary

Type: new-feature
Difficulty: Easy
Recommendation: Adapt

Upstream added a COCOINDEX_APPLICATION_FOR_TRACKING environment variable that, when set to a non-empty value, includes an application field in every telemetry event payload. This lets applications self-identify in aggregate telemetry without changing the default behavior (field is skip_serializing_if = "Option::is_none"). The value is read once at telemetry::init() and stored on TelemetryContext.

Upstream References

• PR: feat(telemetry): add optional application label via env var cocoindex-io/cocoindex#1992
• Release: v1.0.6
• Upstream repo: https://github.com/cocoindex-io/cocoindex

Relevant Upstream Files / Areas

• rust/cocoindex/src/telemetry.rs — adds application: Option<String> to TelemetryContext, reads env var at init(), serializes with skip_serializing_if

Recoco Considerations

• Affected files: crates/recoco-core/src/telemetry.rs (or equivalent telemetry module)
• Adaptation: Rename the env var to RECOCO_APPLICATION_FOR_TRACKING to match recoco's naming conventions instead of COCOINDEX_APPLICATION_FOR_TRACKING
• API: Read once at telemetry::init(), store as Option<String> on the context struct, serialize with skip_serializing_if = "Option::is_none"
• No Python code to exclude; no feature-gating required

Integration Notes

Isolated, low-risk change (~15–20 lines). Adapt by renaming the env var constant to use the RECOCO_ prefix. The upstream test send_event_includes_application_when_set can be ported directly with the renamed constant. Also add a test for the absent-by-default behavior.