Add comprehensive type annotations and Python 3 modernization

[Copilot]

Adds comprehensive type annotations to the Cython source file (_lensfun.pyx) to match the approach in rawpy PR #275. This complements the existing .pyi stub file with runtime-visible type information.

Changes

Typing imports

• Added from typing import Optional, List, Union, Any
• Added from numpy.typing import NDArray

Full type annotations

• Parameter type annotations on all methods: maker: Optional[str], loose_search: bool, etc.
• Return type annotations on all methods and properties
• Database methods: find_cameras() -> List[Camera], find_lenses() -> List[Lens], etc.
• Lens interpolation methods: -> Optional[LensCalibDistortion], etc.
• Modifier apply methods: -> Optional[NDArray[np.float32]] for coordinate arrays, -> bool for color modification

Modern property syntax

• Converted all 34 properties from legacy property abc: syntax to modern @property decorator
• Added return type annotations to all properties (e.g., @property def maker(self) -> str:)
• Properties now use direct return statements instead of __get__ methods

Python 3 modernization

• Added language_level=3 directive to make code Python 3 only
• Removed legacy _chars function (Python 2 compatibility code)
• With c_string_type=unicode and language_level=3, Cython automatically handles str→char* conversion with UTF-8 encoding
• Simplified code by removing manual string encoding calls

Example

import lensfunpy
import numpy as np

db = lensfunpy.Database()
cameras = db.find_cameras('NIKON', 'D3S')  # List[Camera] with full type info

# Modern property access with type information
cam = cameras[0]
maker: str = cam.maker  # Type checker knows this is str
crop: float = cam.crop_factor  # Type checker knows this is float

lens = db.find_lenses(cam, 'Nikon')[0]
mod = lensfunpy.Modifier(lens, cam.crop_factor, 1000, 1000)
mod.initialize(28.0, 2.8)

coords = mod.apply_geometry_distortion()  # Optional[NDArray[np.float32]]
if coords is not None:
    print(coords.shape)

The inline types and modern property syntax improve IDE experience and make type information visible in the compiled module's introspection. The code is now Python 3 only and follows current Cython best practices.

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[letmaik]

@copilot change all legacy property abc: syntax to the modern @property syntax that cython supports, and add return types then to those.

[Copilot]

@copilot change all legacy property abc: syntax to the modern @property syntax that cython supports, and add return types then to those.

Converted all 34 properties from legacy property abc: syntax to modern @property decorator with return type annotations. Commit: dcf1a89