chore: bump guppylang to 0.21.6 and cleanup DEVELOPMENT.md

[qartik]

• Part of https://github.com/quantinuum-dev/hugrverse/issues/241

[ss2165]

We've intentionally left the upper bound unspecified to decouple selene from guppy/hugr minor updates. Since the hugr interface used by selene is small this is pretty safe.

Guppy already has tested that selene works fine with 3.14 since it is used in the integration tests. I think that is sufficient, this PR can be simply a bump in the guppy commit used by selene tests (since the selene CI does not run any python version other than 3.10 anyway)

[ss2165]

suggest changing PR title/commit description to something like "chore: bump guppylang commit to python 3.14 compatible"

[qartik]

Unsure if we need to wait for a guppylang release. I will let Jake or Seyon merge this.

[qartik]

@jake-arkinstall do you have an opinion on unreleased deps?

[jake-arkinstall]

As a test dependency, I am not fussed. It only comes to bite if the commit vanishes.

I'm primarily concerned about how it impacts guppylang's uv deps, if at all. The recursive dependency is a pain point that I would very much like to eliminate at some point. I know this has bitten a few people in the past.

[qartik]

I'm primarily concerned about how it impacts guppylang's uv deps, if at all.

Unsure if it affects that at all. Guppy is marked as a development dependency here.

If you don't foresee any issue, please merge or let me know otherwise.

[jake-arkinstall]

I believe for local development of guppy it gets pulled into the local workspace - could be wrong. @ss2165 what are your thoughts?

[ss2165]

yeah uv solves dev dependencies and package dependencies the same

guppylang 0.21.6 is about to be released imminently so might as well just wait for that Quantinuum/guppylang#1307

[qartik]

I believe this is now ready for merge.

[ss2165]

Suggested PR/commit name:
"chore: bump guppylang to 0.21.6 and cleanup DEVELOPMENT.md"