Improve datetime support for hv.Bars

[hoxbro]

Todo:

• Add tests
• [ ] Improve padding Will postpone this for now
• Look at matplotlib backend

---

Fixes #6364

import holoviews as hv
import pandas as pd

hv.extension("bokeh")

data = pd.DataFrame(
    {"x": pd.date_range("2017-01-01", "2017-01-03", tz="UTC"), "y": [0, 2, -1]}
)

bars = hv.Bars(data, ["x"], ["y"])
hv.Overlay([bars])

---

Fixes #6288

import datetime as dt

import holoviews as hv
import pandas as pd

data = pd.DataFrame(
    {
        "x": pd.to_datetime(
            [
                "2017-01-01T00:00:00",
                "2017-01-01T00:00:00",
                "2017-01-01T01:00:00",
                "2017-01-01T01:00:00",
            ]
        ),
        "cat": ["A", "B", "A", "B"],
        "y": [0, 1, 2, 3],
    }
)
hv.Bars(data, ["x", "cat"], ["y"]).opts(stacked=True)

--
Old issues which was fixed by the implementation.
Resolves #2156

[codecov]

Codecov Report

Attention: Patch coverage is 95.45455% with 2 lines in your changes missing coverage. Please review.

Project coverage is 88.50%. Comparing base (6a96433) to head (67e55f2).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
holoviews/plotting/mpl/chart.py	88.88%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6365   +/-   ##
=======================================
  Coverage   88.49%   88.50%           
=======================================
  Files         323      323           
  Lines       68178    68204   +26     
=======================================
+ Hits        60336    60362   +26     
  Misses       7842     7842           

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