Prepare for v4.0.0 release

[camUrban]

Work to prepare for releasing the latest version!

Changes

• Bumped version numbers
• Fixed typo in README.md
• Fixed mypy errors that only appear with the --strict flag (we're continuing to run mypy without this flag for CI and development, but I figured it couldn't hurt)

Change Magnitude

Minor: Small change such as a bug fix, small enhancement, or documentation update.

---

Checklist

• My branch is based on main and is up to date with the upstream main branch.
• All calculations use S.I. units.
• Code is formatted with black (line length = 88).
• Code is well documented with block comments where appropriate.
• Any external code, algorithms, or equations used have been cited in comments or docstrings.
• All new modules, classes, functions, and methods have docstrings in reStructuredText format, and are formatted using docformatter (--in-place --black).
• All new classes, functions, and methods use type hints.
• If any major functionality was added or significantly changed, I have added or updated tests in the tests package.
• Code locally passes all tests in the tests package.
• After pushing, PR passes all automated checks (codespell, black, mypy, and tests).
• PR description links all relevant issues and follows this template.

---

[Copilot]

Pull request overview

This PR prepares the codebase for a v4.0.0 release by bumping version numbers, fixing a typo in the README, and resolving mypy strict mode type checking errors.

• Version numbers updated from 3.2.0 to 4.0.0 across configuration files
• Corrected typo in README.md ("airfoil" → "airfoils")
• Added specific Callable type signatures and type ignore comments to satisfy mypy --strict mode

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
setup.cfg	Updated package version to 4.0.0
make_installer.iss	Updated installer version to 4.0.0
README.md	Fixed grammar: "airfoil" to "airfoils"
pterasoftware/output.py	Added type ignore comments for webp.Image.fromarray calls
pterasoftware/movements/wing_movement.py	Added explicit Callable type signatures for spacing parameters
pterasoftware/movements/wing_cross_section_movement.py	Added explicit Callable type signatures for spacing parameters
pterasoftware/movements/operating_point_movement.py	Added numpy import and explicit Callable type signature
pterasoftware/movements/airplane_movement.py	Added explicit Callable type signatures for spacing parameters
pterasoftware/movements/_functions.py	Added explicit Callable type signature for custom_function parameter
pterasoftware/geometry/airplane.py	Added type ignore comment for webp.Image.fromarray call
pterasoftware/_parameter_validation.py	Updated return types with explicit Callable signatures and changed list to list[Any]
pterasoftware/_functions.py	Added type ignore comments for @njit decorators
pterasoftware/_aerodynamics.py	Added type ignore comments for @njit decorators