feat: Gpt 5.1 shell tool support

[priyansh4320]

Why are these changes needed?

this PR adds support for GPT 5.1 shell tool support on OAI responses

Related issue number

#2229

Checks

• I've included any doc changes needed for https://docs.ag2.ai/. See https://docs.ag2.ai/latest/docs/contributor-guide/documentation/ to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov]

Codecov Report

❌ Patch coverage is 37.01923% with 131 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
autogen/oai/openai_responses.py	32.25%	52 Missing and 11 partials ⚠️
autogen/tools/shell_tool.py	38.23%	61 Missing and 2 partials ⚠️
autogen/code_utils.py	0.00%	4 Missing and 1 partial ⚠️

Files with missing lines	Coverage Δ
autogen/oai/client.py	54.94% <100.00%> (-3.46%)	⬇️
autogen/code_utils.py	73.06% <0.00%> (+10.28%)	⬆️
autogen/oai/openai_responses.py	58.22% <32.25%> (-11.87%)	⬇️
autogen/tools/shell_tool.py	38.23% <38.23%> (ø)

... and 17 files with indirect coverage changes

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