Full mock coverage

[weswalla]

an hdk_crud refactor to be able to mock all the exposed functions for unit testing on the consumer side.

closes #12

• convert all inner_ crud functions into generic actions
• update comments to describe the generic actions
• use mock feature
• make the remaining hdk_crud functions mockable (turn into struct methods)

Follow ups (split into separate issue and PR)

• write unit tests for remaining functions: Complete Code Test Coverage #1
• fetchers constructor: implement a constructor function for Fetchers for convenience, either new() or default() that constructs a Fetcher #11

[weswalla]

make remaining hdk_functions mockable

current plan:

1. split remaining functions in retrieval.rs into their own file and make them mockable (like get_latest_for_entry.rs)
   

2. make generic crud action functions (in crud.rs) mockable.

• question: each function will become a struct method such that it can be mocked. Should these structs be defined in crud.rs, or split into their own files like the other mocked functions?

[Connoropolous]

@WFinck97
I'm thinking...
along with 'retrieval' which already exists, there could be chain_actions mod...
in it would be a file for create_action update_action delete_action. Separated because these actions affect the source chain

[Connoropolous]

I think all my change requests are expressed as mergeable suggestions.
You can use the bulk 'add suggestion to batch' feature to merge them all at once.

So close! Excellent

[Connoropolous]

would prefer these to be in a spot like 'types' or something, but not going to ask that to be done right now.