Wallet docs

[fkrause98]

Related Issue: #115

Changes:

• Add doctests for the wallet module, with some examples that should compile, taking inspiration from the tests.
  These doctests are only documentative, they compile just fine but most require a working Provider to work.

How to test:

• Checkout to this branch.
• Run cargo test --doc, it should compile the wallet module doc tests.
• Check the docs render properly with cargo doc && open target/doc/zksync_web3_rs/index.html

[codecov-commenter]

Codecov Report

Merging #114 (fc3c611) into main (fd7adf6) will not change coverage.
Report is 1 commits behind head on main.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #114   +/-   ##
=======================================
  Coverage   68.15%   68.15%           
=======================================
  Files          18       18           
  Lines        2179     2179           
=======================================
  Hits         1485     1485           
  Misses        694      694           

Files Changed	Coverage Δ
src/zks_wallet/requests/call_request.rs	78.57% <ø> (ø)
src/zks_wallet/requests/deploy_request.rs	81.81% <ø> (ø)
src/zks_wallet/requests/transfer_request.rs	84.61% <ø> (ø)
src/zks_wallet/requests/withdraw_request.rs	75.00% <ø> (ø)
src/zks_wallet/wallet.rs	54.87% <ø> (ø)

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