Add caching options

[dbrakenhoff]

This allows overriding caching behavior using nlmod.config.NLMOD_CACHE_OPTIONS. This allows you to turn off the hash checks, and optionally activate an explicit dataset coordinate comparison. This allows some more flexibility when running into issue #389.

Recommended usage:

import nlmod

# ... define some ds

# temporarily turn off dataset coordinate hash check and turn on explicit check
with nlmod.config.cache_options(
    dataset_coords_hash=False,
    explicit_dataset_coordinate_comparison=True,
):
    nlmod.read.ahn.get_ahn(ds, cachename="ahn", cachedir=".")

add config submodule

• define NLMOD_CACHE_OPTIONS
• set defaults (identical to current caching defaults)
• add context manager for cache options
• add functions to set, get and reset options.

in cache.py

• add check for global setting in NLMOD_CACHING_OPTIONS
• add logging when global config modifies default
• do not check hashes if global option overrides cache decorator setting
• add explicit dataset coordinate check, useful if hash checks are disabled.

[OnnoEbbens]

Just one comment and then you are good to go, should be an easy fix

[dbrakenhoff]

Good point about only invalidating the cache. This is the output now when you turn on the explicit coordinate check:

While writing this I realize that the caching should be as quiet as possible, so these ERROR messages should be downgraded to INFO I think. I think it is good to know why the cache is being invalidated once you choose this explicit route? But I could also live with DEBUG level. Lemme know what you think.

[dbrakenhoff]

I went for full debug level logging in the excplicit check.

Also, I removed "area" from the data set variables in ds_contains(). I think this was put there for resampling AHN data, but I think this variable can be easily computed if it does not yet exist.

I think this is good to go now.