[ENH] Add units for stored properties

[lmmentel]

See discussion #162

TODO

• update documentation with guide on accessing properties with units

[Copilot]

Pull Request Overview

Adds pint-based unit support for stored ORM properties and related tests

• Introduces UnitMixin and a global UnitRegistry in models.py to enable <attribute>_u accessors returning pint.Quantity
• Updates element, isotope, ionic radius, ionization energy, phase transition, and scattering factor classes to mix in UnitMixin
• Adds unit tests in tests/test_units.py, updates dependencies (pint) and CI (POETRY_VERSION), and a new timeimport dev task

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/test_units.py	Added tests for _u-suffixed unit accessors
tasks.py	Added timeimport task to measure import performance
pyproject.toml	Added pint dependency
mendeleev/models.py	Introduced UnitRegistry, UnitMixin, and updated ORM classes
.github/workflows/main.yml	Bumped Poetry version in CI environment

Comments suppressed due to low confidence (5)

.github/workflows/main.yml:4

• The env section should define a mapping rather than a list item; ensure correct indentation and remove any leading - so CI reads this variable.

POETRY_VERSION: 2.1.3

tasks.py:137

• [nitpick] The new timeimport task lacks a docstring. Consider adding one to describe its purpose and usage.

@task

tests/test_units.py:174

• Tests cover stored properties but omit computed unit properties such as boiling_point_u and melting_point_u. Consider adding tests for these _u accessors.

# methods

mendeleev/models.py:1200

• Typo in half_life_u: using self.half_file instead of self.half_life will raise an AttributeError. Change to self.half_life.

return self.half_file * ureg(self.half_life_unit)

mendeleev/models.py:88

• The code uses enum.Enum but enum is not imported. Add import enum at the top of the file.

class ValueOrigin(enum.Enum):