fix(telemetry): attribute internal SDK calls to their caller module

[jplbrun]

Disclaimer: Do not include SAP-internal or customer-specific information in this PR (e.g. internal system URLs, customer names, tenant IDs, or confidential configurations). This is a public repository.

Description

When one SDK module calls another under the hood, the resulting OpenTelemetry metric was emitted with sap.cloud_sdk.source="user-facing" — indistinguishable from a real customer call. This double-counted customer activity in usage dashboards.

Canonical example: AgentGatewayClient.list_mcp_tools() internally calls destination.get_destination(...) to resolve auth tokens for MCP servers. Before this PR, that internal call was billed as if a customer had directly called get_destination themselves.

This PR fixes that by:

1. Callee-side — adds _telemetry_source support to the two factories that get called internally today: destination (all three factories: create_client, create_fragment_client, create_certificate_client) and agentgateway.create_client. Each factory forwards it to the client constructor, which stores it as self._telemetry_source.

2. Caller-side — passes _telemetry_source=Module.<caller> at every internal cross-module call site:

   • agentgateway/_lob.py:91 → Module.AGENTGATEWAY
   • agentgateway/_fragments.py:38 → Module.AGENTGATEWAY
   • extensibility/client.py:615 → Module.EXTENSIBILITY
   • extensibility/_ums_transport.py:452 → Module.EXTENSIBILITY
   • core/data_anonymization/_http_transport.py:366 and :379 → Module.DATA_ANONYMIZATION
   • core/auditlog_ng/__init__.py:119 → Module.AUDITLOG_NG

Related Issue

N/A

Type of Change

• 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

Unit tests

1. uv run pytest tests/destination/unit/test_init.py -v -k "TelemetrySource" — 6 tests covering the three destination factories.
2. uv run pytest tests/agentgateway/unit/test_agw_client.py -v -k "TelemetrySource" — 2 tests for the agentgateway factory.
3. uv run pytest tests/ -m "not integration" — full unit-test suite. Expected: all tests pass.

End-to-end verification via local OpenTelemetry:

1. Start a local OTLP receiver
2. Drive any flow that transitively hits destination (e.g. AgentGatewayClient.list_mcp_tools).
3. Expected result: the sap.cloud_sdk.source filter shows two values — user-facing (direct customer calls) and agentgateway (internal calls). Before the fix, only user-facing appeared.

Checklist

• 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

None. _telemetry_source is a keyword-only argument with a default of None, so all existing callers of create_client() continue to work unchanged.

Additional Notes

Adding the kwarg to production call sites broke a few pre-existing strict-signature checks. Fixed by loosening them to check only what each test cares about:

• assert_called_once_with(instance=...) → assert_called_once() + call_args.kwargs["instance"] == ...
• lambda: fake_client → lambda **_: fake_client

Both changes decouple the tests from unrelated production kwargs.

[LucasAlvesSoares]