tests(rpc): add backend blocks tests

[danburck]

Part of #1248

Description

This PR adds unit test coverage for the backend blocks.go. It also improves the method names to better represent their function. The unit tests use mocks for client and JSON-RPC client

Note

I noticed, that the method EthBlockFromTendermintBlock has an open todo to add receipts to the block. Currently this endpoint is not used much, so this should be dealt with in a different PR.

[codecov]

Codecov Report

Merging #1296 (9ae3458) into main (7bef408) will increase coverage by 1.36%.
The diff coverage is 52.38%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1296      +/-   ##
==========================================
+ Coverage   55.16%   56.53%   +1.36%     
==========================================
  Files         105      105              
  Lines        9608     9609       +1     
==========================================
+ Hits         5300     5432     +132     
+ Misses       4043     3912     -131     
  Partials      265      265              

Impacted Files	Coverage Δ
rpc/backend/account_info.go	0.00% <0.00%> (ø)
rpc/backend/backend.go	46.66% <ø> (ø)
rpc/backend/call_tx.go	0.00% <0.00%> (ø)
rpc/backend/chain_info.go	10.05% <0.00%> (ø)
rpc/backend/filters.go	0.00% <0.00%> (ø)
rpc/backend/tracing.go	0.00% <0.00%> (ø)
rpc/backend/tx_info.go	0.00% <0.00%> (ø)
rpc/backend/blocks.go	87.76% <80.48%> (ø)

[danburck]

@facs95 I addressed all the changes as we discussed in a call. Will merge now