feat: docs restructure, show_versions, pyright CI, remove 1e-10 zero guards (#7)

* feat(ci): add pyright static type checking

- Fix 4 pyright errors in factor.py (hash annotation, eq/ne override, dead code)
- Add pyright to CI pipeline and dev dependencies
- Remove _resolve_other (dead code after _binary refactor)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* docs: add pyright to all checklists and update changelog for 0.4.0

- PR template: add pyright check item
- README Development section: add pyright command
- CONTRIBUTING: add pyright to verify, dev cycle, and pre-PR checklist
- CHANGELOG [Unreleased]: full list of additions and changes since 0.3.0

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix(core): add missing type hints to _rbinary method

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: quantbai

elvers/core/factor.py

@@ -68,7 +68,7 @@ def _binary(self, other: Factor | int | float, op, op_sym: str) -> Factor:
         )
         return Factor(result, f"({self._name}{op_sym}{other})")
 
-    def _rbinary(self, other, op, op_sym) -> Factor:
+    def _rbinary(self, other: Factor | int | float, op, op_sym: str) -> Factor:
         result = self._df.with_columns(
             op(pl.lit(other), pl.col("factor")).alias("factor")
         )