Fix nested resources dropping their path part (405 on responses/feedback/links/entries/metadata/members)

[nycomp]

Summary

Nested Resource classes were constructed without their path part, so their paths collapsed onto the parent resource's path. Any collection-style call (responses.add(...), feedback.add(...), links.add(...), timetable Entries/Metadata, circle members) hit the parent resource's URL with the wrong method and failed with 405 Method Not Allowed.

Fixes #38

Changes

• Pass the path part at construction for all nested resources:
  • Submission.Responses("responses"), Submission.Feedback("feedback")
  • Assignment.Links("links")
  • Timetable.Entries("entries"), Timetable.Metadata("metadata")
  • Circle.CircleMembers("members") — same root cause as Nested resources drop the parent path: Submission.responses/feedback and Assignment.links POST to the parent URL (405) #38, not listed in the issue
• Drop end_slash=True from Entries.list() / Metadata.get() so they request the leaf routes (/timetable/<id>/entries, /timetable/<id>/metadata) without trailing slashes — otherwise these would 404 against the API's Flask routes
• Pass Assignments.list() filters via the client's query argument (the old params= kwarg raised TypeError: CampusRequest.get() only accepts query)

All corrected request paths verified against the Campus API routes (campus-suite, weekly branch):

Call	Request path
submissions[id].responses.add(...)	POST /api/v1/submissions/<id>/responses
submissions[id].feedback.add(...)	POST /api/v1/submissions/<id>/feedback
submissions[id].submit()	POST /api/v1/submissions/<id>/submit
assignments[id].links.add(...)	POST /api/v1/assignments/<id>/links
timetable[id].entries.list()	GET /api/v1/timetable/<id>/entries
timetable[id].metadata.get()	GET /api/v1/timetable/<id>/metadata
circles[id].members.list()	GET /api/v1/circles/<id>/members

Testing

• Added tests/unit/test_nested_resources.py: 15 regression tests covering path construction and actual request targets for every nested resource
• Full suite passes locally: 73/73 (poetry run pytest, same as CI)
• Issue Nested resources drop the parent path: Submission.responses/feedback and Assignment.links POST to the parent URL (405) #38 reproduction now yields /api/v1/submissions/<id>/responses instead of the collapsed parent path

Out of scope (follow-up)

CircleMembers.add/remove still target the bare /members URL and send an "access" payload key, while the API expects POST /members/add / DELETE /members/remove with access_value; members.list() also unwraps resp.json()["members"] though the API returns the flat mapping directly. These are a separate endpoint-conformance defect from the path collapse fixed here and deserve their own issue.