Support full certificate chain loading from CA bundles (#279)

[octoaide]

Closes #279

Summary

This PR updates the CA-loading logic so that to_ca_certs() parses and loads all PEM certificates found in a provided CA bundle file instead of stopping after the first PEM block. Many users supply CA bundles containing multiple certificates (root + intermediates or multiple roots for different services), and only loading the first certificate caused TLS verification failures for servers relying on subsequent certificates in the bundle.

What changed

• Updated src/client.rs to iterate through all certificates returned from the PEM parser and add each one to the root store (previously only the first cert was added).
• Added tests and a sample CA bundle (tests/ca_cert_bundle.pem) to cover single-file single-cert, single-file multi-cert, multiple files, and empty-input cases.
• Updated CHANGELOG.md with an Unreleased entry documenting the bug fix.

Why

Loading the full certificate chain from CA bundles ensures proper trust chain verification when intermediate or multiple CA certificates are present in the same file. This preserves backward compatibility for single-certificate files while fixing failures caused by incomplete CA loading.

Files changed (high level)

• Modified: src/client.rs (iterate and add all parsed certs)
• Added: tests/ca_cert_bundle.pem (test bundle with multiple certs)
• Modified: CHANGELOG.md (document fix)

Testing

• Added and ran unit tests covering multiple scenarios. All tests pass locally (e.g., cargo test --all-features).

References

• Original issue: Support full certificate chain loading from CA bundles #279

This change uses the auto-closing keyword above to close the referenced issue when merged.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 7.93%. Comparing base (4e1dd53) to head (2c5651b).

Additional details and impacted files

@@            Coverage Diff            @@
##             main    #282      +/-   ##
=========================================
- Coverage   10.19%   7.93%   -2.26%     
=========================================
  Files           8       7       -1     
  Lines         628     529      -99     
=========================================
- Hits           64      42      -22     
+ Misses        564     487      -77     

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[JonghoKim-jj]

I'll review this PR after #274 is merged.