apollo_propeller: add rate-limited queue length warnings

[sirandreww-starkware]

Note

Low Risk
Logging-only behavior change with minimal functional impact; main risk is added log noise or small runtime overhead under sustained backlog conditions.

Overview
Adds apollo_infra_utils as a dependency for apollo_propeller and uses warn_every_n_ms! to emit rate-limited warnings when the handler’s send_queue or events_to_emit exceeds a configurable threshold.

Also adds constants to tune the backlog threshold/interval and documents a potential starvation issue in poll_send when CONCURRENT_STREAMS is increased above 1.

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[sirandreww-starkware]

• apollo_propeller: add minimal config #11196 : 2 dependent PRs (#11197 , #11942 )
• apollo_propeller: add behaviour skeleton #11195
• apollo_propeller: add Event enum to types #11194
• apollo_propeller: add dial upgrade error handling to handler #11074
• apollo_propeller: add rate-limited queue length warnings #11073 👈 (View in Graphite)
• apollo_propeller: add concurrent streams support to handler #11072
• apollo_propeller: implement outbound substream with message batching #11071
• apollo_propeller: add handler helper methods #11070
• main-v0.14.2

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[graphite-app]

Merge activity

• Feb 19, 11:20 AM UTC: This pull request can not be added to the Graphite merge queue. Please try rebasing and resubmitting to merge when ready.
• Feb 19, 11:20 AM UTC: Graphite disabled "merge when ready" on this PR due to: a merge conflict with the target branch; resolve the conflict and try again..

[sirandreww-starkware]

@sirandreww-starkware reviewed 3 files and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on noamsp-starkware).