refactor(BA-4189): move out of convention session function into valid directory

[kwonkwonn]

resolves #8510 (BA-4189)

Move unnecessary functions which should not be located in api layer(not called from api but only from service) into service layer.

Checklist: (if applicable)

• Milestone metadata specifying the target backport version
• Mention to the original issue
• Installer updates including:
  • Fixtures for db schema changes
  • New mandatory config options
• Update of end-to-end CLI integration tests in ai.backend.test
• API server-client counterparts (e.g., manager API -> client SDK)
• Test case(s) to:
  • Demonstrate the difference of before/after
  • Demonstrate the flow of abstract/conceptual models with a concrete implementation
• Documentation
  • Contents in the docs directory
  • docstrings in public interfaces and type annotations

[Copilot]

Pull request overview

Refactors session-related helper utilities out of the API layer into the session service layer to prevent cyclic imports (api ↔ service) and better align module responsibilities.

Changes:

• Added services/session/utils.py and moved drop_undefined() there.
• Moved overwritten_param_check out of api/session.py into services/session/types.py.
• Updated services/session/service.py imports accordingly and removed the old helper definitions from api/session.py.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

File	Description
src/ai/backend/manager/services/session/utils.py	Introduces a service-layer utility module containing drop_undefined().
src/ai/backend/manager/services/session/types.py	Hosts overwritten_param_check alongside existing session service dataclasses.
src/ai/backend/manager/services/session/service.py	Switches imports from API-layer helpers to service-layer helpers.
src/ai/backend/manager/api/session.py	Removes helper definitions/imports that were contributing to API↔service coupling.

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[Copilot]

services/session/types.py now pulls in trafaret/validators just to host overwritten_param_check. In this codebase, service types.py files appear to be kept as lightweight dataclass/type holders (e.g. services/vfolder/types.py, services/image/types.py), and services/session/types.py is imported by action modules that only need the dataclasses. Consider moving overwritten_param_check into a dedicated module (e.g. services/session/validators.py or schemas.py) so non-validation callers don’t pay the extra import-time dependency/overhead.

[Copilot]

In drop_undefined(), isinstance(v, (Mapping, dict)) is redundant because dict is already a Mapping, and len(newval.keys()) > 0 does extra work. You can simplify to check only Mapping and use a truthiness check (if newval) to avoid allocating the keys() view and computing its length.

Suggested change

	if isinstance(v, (Mapping, dict)):
	newval = drop_undefined(dict(v))
	if len(newval.keys()) > 0: # exclude empty dict always
	if isinstance(v, Mapping):
	newval = drop_undefined(dict(v))
	if newval: # exclude empty dict always