fix-worker-429

[harshang03]

This PR hardens worker submission against Prefect Cloud rate limiting. When a 429 is encountered while fetching a deployment, the worker now backs off with jitter (respecting Retry-After when present), retries up to the configured limit, and then defers the submission without crashing the worker. It also improves retry-after parsing on PrefectHTTPStatusError and keeps deployment reads resilient to HTTP errors.
closes #20488

Checklist

• This pull request references any related issue by including "closes <link to issue>"
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• If this pull request adds new functionality, it includes unit tests that cover the changes
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[codspeed-hq]

Merging this PR will not alter performance

✅ 2 untouched benchmarks

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_{Comparing harshang03:fix-20488-worker-429 (2ef41cc) with main (3457693)}

[github-actions]

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