Fix MCP tool bug by dropping unset parameters from input

[ekzhu]

Resolves #6096

Additionally: make sure MCP errors are formatted correctly, added unit tests for mcp servers and upgrade mcp version.

[victordibia]

Thanks @ekzhu

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 8 lines in your changes missing coverage. Please review.

Project coverage is 76.90%. Comparing base (b5ff7ee) to head (a629a4c).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...ges/autogen-ext/src/autogen_ext/tools/mcp/_base.py	46.66%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6125      +/-   ##
==========================================
- Coverage   76.94%   76.90%   -0.05%     
==========================================
  Files         191      191              
  Lines       13381    13387       +6     
==========================================
- Hits        10296    10295       -1     
- Misses       3085     3092       +7     

Flag	Coverage Δ
unittests	76.90% <50.00%> (-0.05%)	⬇️

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