tests: integration tests with JSON-RPC client

[fedekunze]

• Introduce the testnet command to deploy a local testnet
• Update e2e tests to use the testnet network's JSON-RPC client

[codecov]

Codecov Report

Merging #704 (c638ade) into main (481e3b8) will decrease coverage by 0.76%.
The diff coverage is 0.52%.

@@            Coverage Diff             @@
##             main     #704      +/-   ##
==========================================
- Coverage   56.58%   55.81%   -0.77%     
==========================================
  Files          64       64              
  Lines        5774     5853      +79     
==========================================
  Hits         3267     3267              
- Misses       2307     2386      +79     
  Partials      200      200              

Impacted Files	Coverage Δ
client/testnet.go	0.00% <0.00%> (ø)
rpc/ethereum/types/block.go	50.46% <ø> (+1.37%)	⬆️
rpc/ethereum/types/utils.go	0.00% <0.00%> (ø)
x/evm/types/utils.go	65.00% <100.00%> (ø)