feat: add unix and sse MCP transports

[VasuBansal7576]

Implements unix socket and SSE MCP transports, adds reconnect-once retry for unix/SSE, and adds focused unit coverage.

Description

Adds unix socket and SSE transport support to the MCP client, introduces reconnect-once retry behavior for unix/SSE transient connection failures, and adds focused unit tests for the new transport and retry paths.

Type of Change

• New feature (non-breaking change that adds functionality)

Related Issues

Fixes #6347

Part of #6321

Changes Made

• Added unix and sse transport options to MCPServerConfig
• Added socket_path support and unix socket connection handling via httpx.HTTPTransport(uds=...)
• Added SSE connection support using the MCP Python SDK session lifecycle
• Added reconnect-once retry logic for unix and SSE tool calls on transient connection failures
• Added unit tests for unix transport, SSE transport, retry success, retry exhaustion, and preserved HTTP behavior

Testing

Describe the tests you ran to verify your changes:

• Unit tests pass (uv run --package framework pytest core/tests/test_mcp_client.py core/tests/test_tool_registry.py core/tests/test_mcp_server.py)
• Lint passes (uv run --package framework ruff check core/framework/runner/mcp_client.py core/tests/test_mcp_client.py)

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Screenshots (if applicable)

N/A