Full NRPS support

[eliknebel]

This PR implements the Tool NRPS feature plan in docs/features/tool-nrps/plan.md (Phases 0–3) and adds manual QA
reporting artifacts for Phase 4.

What’s included

• Reworked NRPS service into a structured implementation with:
  • typed endpoint/page models
  • launch-claim parsing and validation
  • scope preflight enforcement
  • structured error mapping with reason atoms and retryability
  • page retrieval with retry support
  • stream and eager fetch-all APIs with max-page guard
  • telemetry events for request/page/membership/error
• Added extracted reusable HTTP helpers for future Tool/Platform reuse:
  • Lti_1p3.Services.HTTP.LinkHeader
  • Lti_1p3.Services.HTTP.QueryFilters
• Preserved legacy API compatibility for:
  • fetch_memberships/2 return shape ({:ok, memberships} | {:error, "Error retrieving memberships"})
  • and marked it as deprecated with migration guidance to newer APIs.
• Updated NRPS docs and feature artifacts:
  • new docs/tool_nrps_guide.md
  • tool NRPS requirement matrix
  • utility extraction doc
  • QA report
  • plan checklist updates
• Updated project docs metadata/changelog:
  • added NRPS guide to ExDoc extras
  • README link to NRPS guide
  • CHANGELOG entries for new NRPS APIs/modules and shared helper extraction

Tests / Verification

• mix format
• mix test (full suite): 136 tests, 0 failures
• mix docs completed successfully (existing upstream ExDoc/Earmark warnings observed)

Follow-up / Manual QA

• External LMS sandbox interoperability validation remains pending (tracked in docs/features/tool-nrps/qa_report.md
  and Phase 4 checklist).