chore: improve core http client usage

[NicoleMGomes]

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

Replaces module-internal HTTP client implementations in the print and auditlog modules with the shared HttpClient + XsuaaAuthProvider from sap_cloud_sdk.core.protocol.http, consistent with how dms already works.

Print service (sap_cloud_sdk/print/_http.py, __init__.py):

• PrintHttp previously held a raw requests.Session and manually constructed Authorization headers via TokenProvider.get_token(). It now accepts an HttpClient instance and delegates all auth and session management to it.
• TokenProvider is retained exclusively for resolve_username() — JWT claim decoding needed to auto-fill PrintTask.username.
• create_client() now wires XsuaaAuthProvider(factory) → HttpClient(base_url, auth_provider) → PrintHttp.

Audit Log (sap_cloud_sdk/core/auditlog/_http_transport.py, config.py):

• HttpTransport previously managed its own OAuth2Session, including token fetching, caching, and rotation detection in _ensure_session(). All of that is now handled by XsuaaAuthProvider inside HttpClient.
• AuditLogConfig gained two computed properties — token_url (derives oauth_url + /oauth/token) and base_url (alias for service_url) — so it satisfies the interface expected by XsuaaAuthProvider.
• The _ensure_session() method and the self.oauth attribute are removed.

All changes are internal. No public API signatures were changed.

Related Issue

Closes #

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

1. Run unit tests for all affected modules:

   uv run pytest tests/print/unit/ tests/core/unit/auditlog/ -v

2. Confirm all 185 tests pass with no failures.
3. Run the full unit suite to check for regressions:

   uv run pytest tests/ -q --ignore=tests/integration

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

Additional Notes

This is a follow-up to #332 (credential rotation support). Cassio's review on that PR noted that print and auditlog still used internal HTTP clients instead of the shared core one. This PR addresses that feedback.

The PrintHttp.__init__ signature changed (config and session parameters removed, http_client: HttpClient added), but PrintHttp is an internal class — it is not exported in __all__ and is not part of the public API.