feat(SPT-38678): headers and proxy

[nikshithkolan]

Note

Adds optional headers and proxies to the Swimlane client and adjusts SSL verification based on HTTP/HTTPS; updates docs and examples.

• Client (swimlane/core/client.py):
  • Add optional headers and proxies parameters to Swimlane.__init__ and apply them to the underlying session.
  • Make SSL verification scheme-aware: disable verify for http, honor verify_ssl for https.
  • Update usage examples to include headers and proxies.
• Docs (docs/examples/client.rst):
  • Add sections demonstrating client-wide custom headers and proxies usage with examples.
• CI:
  • Minor workflow tweak in .github/workflows/build_test.yml (no behavior change).

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