fix(agentgateway): port #230 quality fixes + Nicole review onto smahr/main

[tiagoek]

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

Ports onto smahr/main (PR SAP#220) the work that was incorrectly merged into feat/transparent-tls-smahr:

From SAP#230 (sdk-review quality)

• _TOKEN_FIELD_CLIENT_ID / _TOKEN_FIELD_ACCESS_TOKEN constants in _customer.py
• _LOG_TRANSPARENT_MODE constant in agw_client.py
• raise ... from e on token request httpx.RequestError handlers

From SAP#234 / Nicole review

• Remove src/sap_cloud_sdk/core/_telemetry_compat.py and restore core.telemetry imports
• Revert unnecessary change in tests/agentgateway/unit/test_lob.py

Version left at 0.34.0 (already on smahr/main).

Related Issue

Follow-up for SAP#220

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• Code refactoring

How to Test

1. Confirm _telemetry_compat.py is gone
2. Confirm token field / log constants from fix(agentgateway): address sdk-review quality findings from PR #220 SAP/cloud-sdk-python#230 are present
3. Confirm test_lob.py imports match pre-noise layout

Checklist

• I have read the Contributing Guidelines
• I have followed Conventional Commits for commit messages

Breaking Changes

None.

[tiagoek]

Opened on the wrong repository; will open on SAP/cloud-sdk-python instead.