simplify base flex structure

[michael-petersen]

The original FLEX code had experimental compiled versions in it; for ease of use this PR removes those to a separate branch. This PR should be considered a candidate for v1.0.

[Copilot]

Pull Request Overview

This PR removes alternative Cython and Numba implementations of the FLEX library, simplifying the codebase to maintain only the base implementation. The changes also update repository URLs to reflect the new organization ownership.

• Removes Cython-based implementation (FLEXC class and laguerre_cython module)
• Removes Numba-based implementation (FLEXY class from flexnumba module)
• Updates repository URLs from michael-petersen to ObservationalExpansions

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/flex/laguerre_cython.pyx	Deleted Cython implementation of Laguerre polynomial evaluation functions
src/flex/flexnumba.py	Deleted Numba-based FLEXY class and JIT-compiled Laguerre functions
src/flex/flexcython.py	Deleted FLEXC class that used the Cython Laguerre implementation
src/flex/init.py	Removed imports and exports for FLEXY and FLEXC, keeping only base FLEX class
setup.py	Removed Cython extension configuration and build setup
README.md	Updated repository URLs to new organization (ObservationalExpansions)

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