fix: Improve binning in Series.hist with bin_count when all values are the same

[mcrumiller]

Closes #20030.

I added a skip condition to the test_hist_rand to address "flaky failure" in the same-value case, since including it would increase the complexity of the test. It's easier to just include the separate test.

New behavior uses a unit interval, as it does in the single-value case:

>>> pl.Series([1, 1]).hist(bin_count=2)
shape: (2, 3)
┌────────────┬────────────┬───────┐
│ breakpoint ┆ category   ┆ count │
│ ---        ┆ ---        ┆ ---   │
│ f64        ┆ cat        ┆ u32   │
╞════════════╪════════════╪═══════╡
│ 1.0        ┆ (0.5, 1.0] ┆ 2     │
│ 1.5        ┆ (1.0, 1.5] ┆ 0     │
└────────────┴────────────┴───────┘

I think this could use a further improvement and should probably only have a single bin, but that can be a different discussion.

[mcrumiller]

Why is the PR title check failing?

Edit: the PR regex is:

^(build|chore|ci|depr|docs|feat|fix|perf|refactor|release|test)(\\((python|rust)\\!?(,(python|rust)\\!?)?\\))?\\!?\\: [A-Z].*[^\\.\\!\\?,… ]$

which doesn't allow the message to start with a backtick.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.50%. Comparing base (7c97625) to head (cf4b509).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##             main   #20034    +/-   ##
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  Coverage   79.49%   79.50%            
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  Files        1556     1562     +6     
  Lines      216527   216910   +383     
  Branches     2456     2458     +2     
========================================
+ Hits       172136   172448   +312     
- Misses      43833    43903    +70     
- Partials      558      559     +1     

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