ENH: Continue work on type hinting, add pyright to check type coverage.

[genedan]

Summary of Changes

Continues work on adding type hints. Also adds development dependency Pyright which is used to check the quality of the typing and provide a coverage report.

Fixes some formatting issues in docstring example in triangle.py.

Related GitHub Issue(s)

#486

Additional Context for Reviewers

Sets the Chainladder package in the virtual environment to editable mode via a setting in pyproject.toml. This was required for Pyright to generate the coverage report.

We're currently at 5.4%, so we have quite a ways to go until type completeness. We'll just keep chipping away at it.

---

Note

Medium Risk
Mostly typing/configuration work, but it tightens Common._validate_assumption to raise TypeError for unsupported inputs, which could surface new runtime errors in downstream code paths that previously fell through silently.

Overview
Type checking support was added and packaging/test config updated. This introduces pyrightconfig.json, adds pyright as a dev dependency (and updates uv.lock), ships a py.typed marker, and tweaks pytest discovery (testpaths). Coverage config now excludes if TYPE_CHECKING: blocks.

Core typing work continues across core and development. Several modules add from __future__ import annotations, TYPE_CHECKING imports, and richer type annotations for Development/DevelopmentBase helpers.

Behavioral tightening: Common._validate_assumption is refactored into a typed @staticmethod with explicit elif branches and now raises a clear TypeError for unsupported value types; a new unit test asserts this. Docs: multiple Triangle docstring examples are reformatted into Sphinx .. testcode::/.. testoutput:: blocks.

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[codecov]

Codecov Report

❌ Patch coverage is 89.18919% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.94%. Comparing base (5f23ed5) to head (9358edd).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
chainladder/core/common.py	81.81%	0 Missing and 2 partials ⚠️
chainladder/core/tests/test_triangle.py	80.00%	1 Missing ⚠️
chainladder/development/development.py	93.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #735      +/-   ##
==========================================
+ Coverage   85.25%   85.94%   +0.68%     
==========================================
  Files          85       85              
  Lines        4952     4924      -28     
  Branches      645      637       -8     
==========================================
+ Hits         4222     4232      +10     
+ Misses        521      491      -30     
+ Partials      209      201       -8     

Flag	Coverage Δ
unittests	85.94% <89.18%> (+0.68%)	⬆️

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[cursor]

Cursor Bugbot has reviewed your changes and found 3 potential issues.

There are 4 total unresolved issues (including 1 from previous review).

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