refactor: Remove direct pandas import

[hoxbro]

This PR introduces the utilities _lazy_module and gen_types. Both are meant to depend on 3rd party libraries without using direct imports.

These have been used throughout the code, so pandas is no longer imported directly; this has significantly improved import time and, at the same time, set up the codebase to handle a world where pandas is not the only DataFrame library. Some functionality can likely be rewritten to not depend on pandas, but I will do that in future PRs.

The _lazy_module has also "sneaked" into the Ibis data interface, which, in my opinion, makes it cleaner by not having all methods start with import ibis.

Lastly, I have also removed the use of lazy_isinstance and deprecated it as the functionality can be done with _lazy_module and a bool check. This is done in holoviews/operation/datashader.py.

Some statics:

Hyperfine

Main (0ba7398)

❯ hyperfine "python -c ''" "python -c 'import holoviews'" --warmup 5
Benchmark 1: python -c ''
  Time (mean ± σ):      16.0 ms ±   0.6 ms    [User: 12.0 ms, System: 3.9 ms]
  Range (min … max):    14.9 ms …  17.6 ms    171 runs

Benchmark 2: python -c 'import holoviews'
  Time (mean ± σ):     367.3 ms ±  11.7 ms    [User: 1938.8 ms, System: 57.8 ms]
  Range (min … max):   356.4 ms … 391.3 ms    10 runs

Summary
  python -c '' ran
   22.90 ± 1.10 times faster than python -c 'import holoviews'

This PR (18f4db4)

❯ hyperfine "python -c ''" "python -c 'import holoviews'" --warmup 5
Benchmark 1: python -c ''
  Time (mean ± σ):      16.2 ms ±   0.6 ms    [User: 12.0 ms, System: 4.0 ms]
  Range (min … max):    14.9 ms …  19.1 ms    179 runs

Benchmark 2: python -c 'import holoviews'
  Time (mean ± σ):     189.7 ms ±   9.2 ms    [User: 1781.3 ms, System: 29.2 ms]
  Range (min … max):   182.5 ms … 216.8 ms    15 runs

Summary
  python -c '' ran
   11.74 ± 0.71 times faster than python -c 'import holoviews'

Tuna

Running python -X importtime -c 'import holoviews' 2> tuna.log && tuna tuna.log

Main (0ba7398)

This PR (18f4db4)

Output of hv.show_versions

Python              :  3.13.2 | packaged by conda-forge | (main, Feb 17 2025, 14:10:22) [GCC 13.3.0]
Operating system    :  Linux-6.13.5-arch1-1-x86_64-with-glibc2.41
Panel comms         :  default

holoviews           :  1.20.1.post1.dev7+g95d3af8b2

bokeh               :  3.6.3
colorcet            :  3.1.0
cudf                :  -
cupy                :  13.4.0
dask                :  2025.2.0
dask-expr           :  -
datashader          :  0.17.0.post1.dev5+gc3e4b58
geoviews            :  1.14.0.post1.dev2+gd89e2f7
hvplot              :  0.11.3.dev9+g9700bec.d20250301
ibis-framework      :  10.1.0
IPython             :  8.32.0
ipywidgets-bokeh    :  1.6.0
jupyter-bokeh       :  4.0.5
jupyterlab          :  4.3.5
matplotlib          :  3.10.1
networkx            :  3.4.2
notebook            :  -
numba               :  0.61.0
numpy               :  2.1.3
pandas              :  2.2.3
panel               :  1.6.1.post1.dev4+gf5170c481.d20250301
param               :  2.2.0.post1.dev22+gee19961
pillow              :  11.1.0
plotly              :  6.0.0
pyarrow             :  19.0.1
pyviz-comms         :  3.0.4
scikit-image        :  0.25.2
scipy               :  1.15.2
spatialpandas       :  0.5.0
streamz             :  -
tsdownsample        :  0.1.4.1
xarray              :  2025.1.2

[codecov]

Codecov Report

Attention: Patch coverage is 86.55462% with 32 lines in your changes missing coverage. Please review.

Project coverage is 88.77%. Comparing base (2465ad1) to head (fe84295).

Files with missing lines	Patch %	Lines
holoviews/core/util/dependencies.py	79.66%	12 Missing ⚠️
holoviews/core/util/types.py	92.64%	5 Missing ⚠️
holoviews/core/util/__init__.py	87.50%	4 Missing ⚠️
holoviews/core/data/cudf.py	0.00%	3 Missing ⚠️
holoviews/core/data/pandas.py	86.66%	2 Missing ⚠️
holoviews/element/util.py	66.66%	2 Missing ⚠️
holoviews/core/data/ibis.py	85.71%	1 Missing ⚠️
holoviews/element/graphs.py	50.00%	1 Missing ⚠️
holoviews/operation/datashader.py	90.00%	1 Missing ⚠️
holoviews/streams.py	91.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6476      +/-   ##
==========================================
- Coverage   88.79%   88.77%   -0.03%     
==========================================
  Files         323      325       +2     
  Lines       68949    69090     +141     
==========================================
+ Hits        61225    61333     +108     
- Misses       7724     7757      +33     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.