feat(client): add connect_timeout to bound the connect phase

[fatih-acar]

Summary

An Infrahub endpoint that does not answer the TCP or TLS handshake used to hold every SDK request for the full request timeout (60 seconds by default) before failing. This PR bounds the connect phase separately, so a client behind a DNS round robin or a failing-over load balancer moves on to its next attempt after a few seconds instead of waiting out the whole request budget.

Key Changes

• A new connect_timeout setting (default 10 seconds, INFRAHUB_CONNECT_TIMEOUT) bounds the TCP/TLS handshake on every request path: regular requests, multipart uploads and streaming downloads, on both the async and sync clients. It never exceeds the per-request timeout.
• The timeout setting's description now states what it covers (read, write and pool phases) instead of calling itself a "connection timeout". No behaviour change.

The transient retry handler on stable already treats a connect timeout as a lost connection and retries it when retry_on_failure is enabled, so this PR only shortens how long each failed attempt takes. An earlier revision of this PR also carried that retry mapping; it was dropped during the rebase onto stable.

Documentation Updates

• docs/docs/python-sdk/reference/config.mdx regenerated with the new setting.
• One changelog fragment in changelog/.

Test Plan

• uv run pytest tests/unit/sdk/test_connect_timeout.py covers the config default and validation, the exact timeout httpx receives on every path for both clients, the cap by the request timeout, and that a connect timeout still surfaces as ServerNotReachableError and is retried through execute_graphql.
• uv run invoke format lint-code and uv run invoke docs-validate pass locally.
• The full tests/unit suite passes except three pre-existing infrahubctl table-rendering failures that fail identically on stable.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@            Coverage Diff             @@
##           stable    #1324      +/-   ##
==========================================
- Coverage   84.88%   84.86%   -0.02%     
==========================================
  Files         148      148              
  Lines       13309    13291      -18     
  Branches     1965     1955      -10     
==========================================
- Hits        11297    11280      -17     
  Misses       1442     1442              
+ Partials      570      569       -1     

Flag	Coverage Δ
integration-tests	38.76% <50.00%> (-0.09%)	⬇️
python-3.10	57.72% <50.00%> (+0.07%)	⬆️
python-3.11	57.72% <50.00%> (+0.05%)	⬆️
python-3.12	57.72% <50.00%> (+0.05%)	⬆️
python-3.13	57.72% <50.00%> (+0.07%)	⬆️
python-3.14	57.72% <50.00%> (+0.05%)	⬆️
python-filler-3.12	23.78% <50.00%> (-0.01%)	⬇️

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Files with missing lines	Coverage Δ
infrahub_sdk/client.py	84.06% <100.00%> (+0.02%)	⬆️
infrahub_sdk/config.py	91.61% <100.00%> (+0.05%)	⬆️

... and 2 files with indirect coverage changes

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