feat(sessions): renew, errors policy, and shared transport

[shinybrar]

Summary

• Add Session.renew / AsyncSession.renew and canfar renew to reset interactive Session lifetimes (parity with Science Portal / Skaha action=renew).
• Add client errors / CANFAR_ERRORS and per-call errors= on lifecycle methods, raising SessionRequestError with partial results after every request runs.
• Add caller-owned HTTPClient(transport=...) for shared connection pools (Bearer tokens only; clients never close the transport).

Closes #329

Test plan

• uv run ruff check . --no-cache and uv run ty check canfar
• uv run pytest tests -m "not slow" --no-cov -q
• uv run pytest tests/test_skills.py --no-cov -q -n0
• uv run --group docs mkdocs build
• Manual: canfar renew SESSION_ID renews without a prompt and prints success/failure summaries
• Manual: Session(errors="raise").destroy([...]) raises SessionRequestError with partial results
• Manual: inject httpx2.HTTPTransport / AsyncHTTPTransport and confirm close does not shut down the pool

[codecov-commenter]

Codecov Report

❌ Patch coverage is 97.08333% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.19%. Comparing base (8aafe2e) to head (f9a225f).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
canfar/helpers/session.py	93.22%	4 Missing ⚠️
canfar/cli/renew.py	95.23%	0 Missing and 1 partial ⚠️
canfar/exceptions/session.py	92.30%	0 Missing and 1 partial ⚠️
canfar/sessions.py	98.97%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #331      +/-   ##
==========================================
+ Coverage   90.92%   91.19%   +0.27%     
==========================================
  Files          61       64       +3     
  Lines        4286     4454     +168     
  Branches      508      529      +21     
==========================================
+ Hits         3897     4062     +165     
  Misses        258      258              
- Partials      131      134       +3     

Flag	Coverage Δ
3.10	91.19% <97.08%> (+0.27%)	⬆️
3.11	91.19% <97.08%> (+0.27%)	⬆️
3.12	91.19% <97.08%> (+0.27%)	⬆️
3.13	91.19% <97.08%> (+0.27%)	⬆️
3.14	91.19% <97.08%> (+0.27%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.