(fix): use typesize on Blosc codec

[ilan-gold]

Fixes #2766 and fixes #2171
TODO:

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions
• New/modified features documented in docs/user-guide/*.rst
• Changes documented as a new file in changes/
• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)

[d-v-b]

this looks good @ilan-gold, we just a release note

[ilan-gold]

Apologies did not mean for you guys to do an immediate review, will keep that in mind next time, this was mostly to remind myself to finish up :)

[d-v-b]

no worries, I was trigger-happy here

[dstansby]

Is it worth adding a test for this that asserts a certain compressed size, so we can catch regressions in the future? The doctest is a nice way to catch this, but I worry that it might get removed or changed whereas a test is more likely to stay around.