Migrate the build system to Meson/meson-python

[agriyakhetarpal]

Closes #62
Closes #188
See also #6; this adds testing for the editable installation. Might be overkill, but it was a good way to learn what Meson was doing.

cc: @ulgens; if you'd like to take a look! Sorry if you wanted to take this – I woke up super enthusiastic today and decided today's the day to tackle it once and for all :D

• CI passes
• Experimental Zig CI builds have correct platform tags
• wheel size is not abnormally large
• sdist is not greater than 10 MiB (and has reduced, in fact)
• CD passes (triggered at https://github.com/agriyakhetarpal/hugo-python-distributions/actions/runs/24947637020 and sizes are identical to https://pypi.org/project/hugo/0.160.1/#files)
• Update docs

[ulgens]

Woohoo 😄 I planned my day for another FOSS project and I won't be able to check it today but I'll try to chime in in the next couple days.

[agriyakhetarpal]

Absolutely, of course!

[agriyakhetarpal]

Note to self: see if we can implement expanding {project} in cibuildwheel for CIBW_CONFIG_SETTINGS, too.

[agriyakhetarpal]

(Last three commits were authored with AI assistance, BTW)

[agriyakhetarpal]

Okay, at this point we're at the stage where the editable installations and the regular installation tests work all fine, just that we're stuck because of the mixed layout of the Hugo executable landing in a platdir and _version.py landing in purelib, which auditwheel is not happy with. delocate and delvewheel are alright with this.