feat: Request retry for 429 and 503 responses with exponential backoff

[andrespd99]

Description

This PR adds automatic request retry with backoff for retryable responses (429 and 503) and customizable parameters.

Changes

Rewrote Client.do to:

• Ensure request bodies are replayable (set GetBody when missing).
• Retry up to Client.maxRetries times on HTTP 429 and 503 with exponential backoff and jitter.
• Drain and close response bodies for intermediate 429/503 responses so connections can be reused.
• Leave the final 429/503 response body intact so makeHTTPClientError can read it.

Notes and rationale

• I preserved behavior for non-retryable non-2xx responses by returning makeHTTPClientError immediately.
• For requests with bodies, I set req.GetBody so each attempt can get a fresh Body reader. This matches how http expects retryable requests to behave.
• Kept default backoff values conservative (base 100ms, 3 retries). These can be tuned or made configurable if user wants.
• I avoided closing the response in the final failed attempt so makeHTTPClientError can read the body (it calls io.ReadAll).

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

❌ Patch coverage is 45.31250% with 35 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.22%. Comparing base (b19a753) to head (8228548).

Files with missing lines	Patch %	Lines
client.go	46.77%	26 Missing and 7 partials ⚠️
errors.go	0.00%	2 Missing ⚠️
❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #28      +/-   ##
==========================================
- Coverage   79.59%   76.22%   -3.38%     
==========================================
  Files           9        9              
  Lines         446      408      -38     
==========================================
- Hits          355      311      -44     
- Misses         68       70       +2     
- Partials       23       27       +4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.