Cleanups of the storage definitions.

[MathieuDutSik]

Motivation

In PR #2896 it was suggested to move the definition of the stores to mod.rs. Ultimately, this is not what is done in this PR as there was disagreement.

Proposal

The following was done:

• Simplify out the relevant code from the stores, in particular the LocalStackTestContext that is no longer used.
• Remove unused enum in the error types, that is MissingDatabase and AlreadyExistingDatabase.
• Introduce constructor for the RocksDbStoreConfig and similar.
• Remove the pub attribute when not needed.
• Correct the mis-attribution "lru splitting" into "lru caching".
• Add a PathWithStorage function and remove another function.
• Put the constructor definition of the VISIBLE_MAX_VALUE_SIZE for DynbamoDb and remove the test that simply reproduce the formula.
• The InvalidTableName was renamed as InvalidNamespace.

Test Plan

CI as the functionality should stay exactly the same.

Release Plan

Not relevant.

Links

None.

[afck]

I like the simplifications using the constructors (like DynamoDbStoreConfig::new). 👍

But I'd prefer to keep types specific to different backends in different modules, personally.

[afck]

We could still have these in separate submodules and re-export them, to reduce the number of cfg statements.

In general I'm not sure if moving these directly into backends is an improvement.

[MathieuDutSik]

I like the simplifications using the constructors (like DynamoDbStoreConfig::new). 👍

But I'd prefer to keep types specific to different backends in different modules, personally.

Ok, we will have to see what @ma2bd thinks as it was his initial suggestion. I like the separation.

[MathieuDutSik]

I like the simplifications using the constructors (like DynamoDbStoreConfig::new). 👍

But I'd prefer to keep types specific to different backends in different modules, personally.

That is indeed a little problematic. So, I revamped the PR by focusing on less controversial issues that hopefully could be accepted more easily.