Document the behavior of converting a Dask array to a Python number

[bouweandela]

Document the behavior when converting Dask arrays to Python numbers (bool/int/float/complex): https://dask--10686.org.readthedocs.build/en/10686/array-api.html#array

I noticed that there was some discussion on whether or not this is a desirable feature in #9387, but I thought it would be useful to document it anyway as this will help to avoid confusion.

For us, this feature is quite useful because it allows us to write e.g.

if a.any():
    do_something()

and that will work regardless of whether a is a numpy or a Dask array.

• Closes #xxxx
• Tests added / passed
• Passes pre-commit run --all-files

[GPUtester]

Can one of the admins verify this patch?

Admins can comment ok to test to allow this one PR to run or add to allowlist to allow all future PRs from the same author to run.

[github-actions]

Unit Test Results

See test report for an extended history of previous test failures. This is useful for diagnosing flaky tests.

     15 files  +     12       15 suites  +12   3h 26m 42s ⏱️ + 3h 21m 39s
 12 941 tests +  7 769   11 675 ✅ +  7 272     929 💤 +   160  337 ❌ +337 
160 329 runs  +153 166  143 060 ✅ +137 082  16 932 💤 +15 747  337 ❌ +337 

For more details on these failures, see this check.

Results for commit db2b3bc. ± Comparison against base commit dde25d9.