DOCS: Request type hints in pull requests

[EKtheSage]

Summary

• ask contributors to add type hints to new or modified Python code where applicable
• update the pull request template to make the guidance visible for every contribution

Closes #1043

Test plan

• Reviewed the rendered Markdown structure
• No automated tests needed for a pull request template text change

---

Note

Low Risk
Template-only documentation change with no runtime or CI behavior impact.

Overview
Updates .github/pull_request_template.md so every PR reminds contributors to add type hints to new or modified Python code where applicable.

The note sits under Additional Context for Reviewers; existing checklist items are unchanged.

^{Reviewed by Cursor Bugbot for commit 22e196d. Bugbot is set up for automated code reviews on this repo. Configure here.}

[github-actions]

Pyright Type Completeness

View the full pyright --verifytypes output for this commit

Project (full chainladder package, at this PR's head): 14.6% of exported symbols fully typed (185 / 1271)

	Known	Ambiguous	Unknown	Total
Project (head)	185	106	980	1271

Other symbols referenced but not exported by chainladder: 13

	Known	Ambiguous	Unknown	Total
Other (head)	3	1	9	13

Symbols without documentation:

• Functions without docstring: 313
• Functions without default param: 0
• Classes without docstring: 10

Patch (exported symbols added or changed by this PR): no exported symbol type-completeness changes detected.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.50%. Comparing base (990dc9e) to head (22e196d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1106   +/-   ##
=======================================
  Coverage   90.50%   90.50%           
=======================================
  Files          91       91           
  Lines        5289     5289           
  Branches      671      671           
=======================================
  Hits         4787     4787           
  Misses        359      359           
  Partials      143      143           

Flag	Coverage Δ
unittests	90.50% <ø> (ø)

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