Added ZkSync methods

[smickovskid]

• Added ZkSync methods

[friedemannf]

I added an override for the funding/refunding logic for zkSync. I wasn't sure whether to opt for duplicating code or changing the existing implementation on EthereumClient but chose the former for now. Maybe it would make more sense for

func attemptReturn(e *EthereumClient, fromKey *ecdsa.PrivateKey, attemptCount int) (*types.Transaction, error)

to accept an interface? Thereby we could prevent having the same code twice.

[codecov-commenter]

Codecov Report

Attention: 158 lines in your changes are missing coverage. Please review.

Comparison is base (368aa75) 31.13% compared to head (a1c6b64) 30.24%.

Files	Patch %	Lines
blockchain/zksync.go	0.00%	156 Missing :warning:
blockchain/known_networks.go	0.00%	2 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #714      +/-   ##
==========================================
- Coverage   31.13%   30.24%   -0.90%     
==========================================
  Files          41       42       +1     
  Lines        5361     5519     +158     
==========================================
  Hits         1669     1669              
- Misses       3512     3670     +158     
  Partials      180      180              

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