[WIP] Add explicit deletion to contexts in ContextCache on empty

[dotsdl]

Description

Note: this may not be sufficient; will need to investigate that it
actually succeeds in clearing contexts.

Todos

• Implement feature / fix bug
• Add tests
• Update documentation as needed
• Update changelog to summarize changes in behavior, enhancements, and bugfixes implemented in this PR

Status

• Ready to go

Changelog message

[codecov]

Codecov Report

Merging #690 (49f2e1d) into main (b379af3) will increase coverage by 0.00%.
The diff coverage is 100.00%.

[dotsdl]

This may not be finished yet; please do not merge.

[jchodera]

This should address #688

[ijpulidos]

We want to write tests that creates many context caches and make sure that the resources of the GPU don't get depleted (if we are emptying the context cache correctly). First we test this locally and then in the GPU CI.

We need GPU CI testing for this.

[ijpulidos]

After the basic test we can also create a replica exchange sampler test where we create and destroy many repex samplers and check if the GPU resources are correctly handled.

Minimizers might be creating their own context. We can give it a pre-minimized structure or tell it to do only one minimization step (using the multistatesampler minimize method)

[jchodera]

We also need a __del__ that calls empty().