[Access] Properly handle subscription errors in data providers

[illia-malachyn]

Originally, the description of the issue was like that

Distinguish between `context.Canceled` errors originating from the streamer and those triggered by the DataProvider’s `Close()` method.

1. I Added `closeChan` that is used in `DataProvider.Close()` method to indicate `DataProvider.Run()` that users of data providers (WebSocket controller in our case) want to finish receiving data. 
2. `HandleSubscription()` function is replaced by `run()` function that is aware of `closeChan`. I made a new function for it because `HandleSubscription()` is widely used in the access package (`HandleRPCSubscription` has 22 usages atm).
3. `run()` returns nil if `closeChan` was closed. `HandleSubscription` returned `ctx.Canceled` which lead to confusion as `ctx.Canceled` could come from 2 sources (streamer and websocket controller).
4. I did a little refactoring to a bunch of `sendResponse()` functions to make it more readable.

However, after a couple of discussions and work on that, I can conclude that the first 3 clauses are outdated and were removed from the implementation. The only thing we left is the refactoring and the fact that we start the ubscription after a Run() method has been called.

Closes #7040 #7047

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 84.34505% with 49 lines in your changes missing coverage. Please review.

Project coverage is 41.25%. Comparing base (82d7f1d) to head (429b961).

Files with missing lines	Patch %	Lines
engine/access/rest/common/models/block.go	47.27%	26 Missing and 3 partials ⚠️
...ss/rest/websockets/data_providers/base_provider.go	67.85%	6 Missing and 3 partials ⚠️
...ockets/data_providers/account_statuses_provider.go	92.68%	2 Missing and 1 partial ⚠️
.../rest/websockets/data_providers/blocks_provider.go	91.42%	2 Missing and 1 partial ⚠️
...ckets/data_providers/mock/data_provider_factory.go	40.00%	3 Missing ⚠️
.../rest/websockets/data_providers/args_validation.go	80.00%	1 Missing ⚠️
.../rest/websockets/data_providers/events_provider.go	97.36%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7046   +/-   ##
=======================================
  Coverage   41.25%   41.25%           
=======================================
  Files        2170     2170           
  Lines      190050   190098   +48     
=======================================
+ Hits        78409    78429   +20     
- Misses     105097   105123   +26     
- Partials     6544     6546    +2     

Flag	Coverage Δ
unittests	41.25% <84.34%> (+<0.01%)	⬆️

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[Guitarheroua]

Looks good to me!

[illia-malachyn]

After discussing with Yurii, we agreed to use a different approach here.

As this will changed, will re-aprove final implementation

[peterargue]

why is this refactor needed? can you point out the important changes, it's not clear to me

[illia-malachyn]

why is this refactor needed? can you point out the important changes, it's not clear to me

Hey. I updated PR's description. Added a context of what has been done and why.

[illia-malachyn]

@peterargue I also pointed out the most important lines of code

[Guitarheroua]

The first round of review - DONE! I have a few small comments.

[Guitarheroua]

Looks good!

[peterargue]

one small improvement, then this is ready to merge