feat(extensibility): add agentExtVersion to extensibility and telemetry

[shubhi1789]

Description

The SDK now reads agentExtensionVersion from UMS and surfaces it on the
ExtensionCapabilityImplementation object returned by
ExtensibilityClient.get_extension_capability_implementation().

This field tracks the agent's current extension version counter — an integer
string (e.g. "5") that increments each time extensions for that agent are
modified in UMS.

The value is also propagated through the full telemetry pipeline — individual
spans, the summary span, OTel baggage, and structured log records.

Type of Change

Please check the relevant option:

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Code refactoring
• Dependency update

How to Test

1. Run the sap-agent-extensinbility skill on the test agent with latest sdk version .
2. Then agent will get latest changes for telemetry for agent extension version

Make request to the agent and it will emit agent ext version in summary and other spans.

Checklist

Before submitting your PR, please review and check the following:

• I have read the Contributing Guidelines
• I have verified that my changes solve the issue
• I have added/updated automated tests to cover my changes
• All tests pass locally
• I have verified that my code follows the Code Guidelines
• I have updated documentation (if applicable)
• I have added type hints for all public APIs
• My code does not contain sensitive information (credentials, tokens, etc.)
• I have followed Conventional Commits for commit messages

Breaking Changes

If this PR introduces breaking changes, please describe:

NA

Additional Notes

NA

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