cmd/pyenv-sync: Create major version symlink(s) to fix pyenv support

[landoncrabtree]

Added proper pyenv support to brew pyenv-sync by symlinking major version executables to their minor.

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This PR aims to fix brew pyenv-sync support. Prior to this, pyenv-sync only symlinks ~/.pyenv/versions/python{major}.{minor}.{patch} to /opt/homebrew/Cellar/python@{major}.{minor}/{major}.{minor}.{patch}. pyenv looks within the bin directory for executables, so by-default, the following executables are in PATH (in this example, for say python@3.12)

2to3-3.12
idle3.12
pip3.12
pydoc3.12
python3.12
python3.12-config
wheel3.12

So, if a user invokes python3 or pip3, it will not be in ~/.pyenv/versions/___/bin and pyenv will fallback to system default (in this case, the latest python3 installation from Homebrew, python3.13). This commit adds additional symlinks: python3, pip3, wheel3, idle3, pydoc3 that way pyenv version management works as expected using python3 and pip3.

See the following for reference on what issue(s) this fixes:

• Homebrew Python linked to Pyenv with brew pyenv-sync is ignored when running python3 pyenv/pyenv#3105
• pyenv does not work with brew pyenv-sync #17563
• https://github.com/orgs/Homebrew/discussions/4664

Looks like it's been an issue for a while (July 2023). The proposed fixes are:

• python formula adds the symlinks themselves
• pyenv adds some sort of detection for Homebrew and checks libexec instead of bin
• Users create the symlinks manually (eg: ln -s ~/.pyenv/versions/3.12.8/bin/python3.12 ~/.pyenv/versions/3.12.8/bin/python3)
• pyenv-sync creates the symlinks (This seems like the most appropriate approach, which is what I have done)

[MikeMcQuaid]

Amazing work, particularly for a first PR! Thanks @landoncrabtree, you rock!