Add restrict_info method for metadata

[sjvenditto]

Complementing the drop_info() method, a restrict_info() method has been added to all objects with metadata. This method allows you to specify which metadata columns to keep, dropping all other metadata columns. For TsGroup objects, rate will always be kept even if it is not specified.

>>> import pynapple as nap
>>> import numpy as np
>>> tmp = {0:nap.Ts(t=np.arange(0,200), time_units='s'),
... 1:nap.Ts(t=np.arange(0,200,0.5), time_units='s'),
... 2:nap.Ts(t=np.arange(0,300,0.25), time_units='s'),
... }
>>> metadata = {"l1": [1, 2, 3], "l2": ["x", "x", "y"], "l3": [4, 5, 6]}
>>> tsgroup = nap.TsGroup(tmp,metadata=metadata)
>>> print(tsgroup)
  Index     rate    l1  l2      l3
-------  -------  ----  ----  ----
      0  0.66722     1  x        4
      1  1.33445     2  x        5
      2  4.00334     3  y        6

>>> tsgroup.restrict_info(["l2", "l3"])
>>> tsgroup
  Index     rate  l2      l3
-------  -------  ----  ----
      0  0.66722  x        4
      1  1.33445  x        5
      2  4.00334  y        6

Class-specific docstring examples have been added, as well as a new section under the Metadata user guide page in the docs

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
pynapple/core/interval_set.py	97.13% <100.00%> (+0.02%)	⬆️
pynapple/core/metadata_class.py	92.42% <100.00%> (+0.31%)	⬆️
pynapple/core/time_series.py	93.33% <100.00%> (+0.02%)	⬆️
pynapple/core/ts_group.py	92.93% <100.00%> (+0.04%)	⬆️

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