fix(auditlog_ng): infer OTLP protocol from endpoint when env unset

[jeanscherf]

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

The Audit Log NG client picked its OTLP transport from OTEL_EXPORTER_OTLP_PROTOCOL, defaulting to gRPC when that variable was unset (_create_log_exporter in src/sap_cloud_sdk/core/auditlog_ng/client.py). In common deployments that variable is never injected, so an HTTP audit endpoint (for example http://host:4318/v1/logs) was always dialed with a gRPC exporter and delivery failed.

This derives the protocol from the resolved config.endpoint instead. New helper _infer_protocol_from_endpoint reads the endpoint shape (an http(s) URL with a path means http/protobuf; a bare host:port means grpc), and _resolve_protocol applies it: an explicit OTEL_EXPORTER_OTLP_PROTOCOL still wins when set, inference is used when it is unset, and gRPC remains the fallback when both the env and the shape are inconclusive.

Related Issue

N/A — no public issue reference.

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. Unset OTEL_EXPORTER_OTLP_PROTOCOL, build AuditClient with endpoint="http://host:4318/v1/logs", and confirm an HTTPLogExporter is constructed (previously a GRPCLogExporter was used).
2. Unset the env and build with endpoint="audit.example.com:443"; confirm a GRPCLogExporter is constructed.
3. Set OTEL_EXPORTER_OTLP_PROTOCOL=grpc with an HTTP endpoint and confirm gRPC is used (explicit override wins).
4. Run uv run pytest tests/core/unit/auditlog_ng/unit/test_client.py -k "Protocol or Infer or Resolve".

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

Design note: an endpoint with no path resolves to gRPC even when it carries an http/https scheme, because a path is the only positive HTTP signal and OTLP/gRPC endpoints legitimately use an http(s) scheme to indicate (in)secure transport. The rare "HTTP base endpoint without /v1/logs" case is covered by setting OTEL_EXPORTER_OTLP_PROTOCOL explicitly. This behavior is pinned by a test.

Unit tests cover every branch of both helpers (http/grpc, with and without port, scheme vs no scheme, no host, empty/None, and the env precedence/fallback paths).

ruff format also normalized a few pre-existing long lines in tests/core/unit/auditlog_ng/unit/test_client.py (imports, a helper signature, one assertion) that were touched by the required pre-commit hook.