Problem: no python and nix format checker in CI

[yihuang]

Closes: #79

• Run flake8 for python
• Run nixpkgs-fmt for nix

👮🏻👮🏻👮🏻 !!!! REFERENCE THE PROBLEM YOUR ARE SOLVING IN THE PR TITLE AND DESCRIBE YOUR SOLUTION HERE !!!! DO NOT FORGET !!!! 👮🏻👮🏻👮🏻

PR Checklist:

• Have you read the CONTRIBUTING.md?
• Does your PR follow the C4 patch requirements?
• Have you rebased your work on top of the latest master?
• Have you checked your code compiles? (make)
• Have you included tests for any non-trivial functionality?
• Have you checked your code passes the unit tests? (make test)
• Have you checked your code formatting is correct? (go fmt)
• Have you checked your basic code style is fine? (golangci-lint run)
• If you added any dependencies, have you checked they do not contain any known vulnerabilities? (go list -json -m all | nancy sleuth)
• If your changes affect the client infrastructure, have you run the integration test?
• If your changes affect public APIs, does your PR follow the C4 evolution of public contracts?
• If your code changes public APIs, have you incremented the crate version numbers and documented your changes in the CHANGELOG.md?
• If you are contributing for the first time, please read the agreement in CONTRIBUTING.md now and add a comment to this pull request stating that your PR is in accordance with the Developer's Certificate of Origin.

Thank you for your code, it's appreciated! :)

[codecov]

Codecov Report

Merging #80 (efe84c9) into main (3ea70c5) will increase coverage by 4.64%.
The diff coverage is 41.83%.

@@            Coverage Diff             @@
##             main      #80      +/-   ##
==========================================
+ Coverage   21.51%   26.15%   +4.64%     
==========================================
  Files          27       32       +5     
  Lines        1729     2183     +454     
==========================================
+ Hits          372      571     +199     
- Misses       1324     1575     +251     
- Partials       33       37       +4     

Impacted Files	Coverage Δ
app/app.go	3.89% <0.00%> (-0.07%)	⬇️
x/cronos/keeper/grpc_query.go	0.00% <0.00%> (ø)
x/cronos/keeper/hooks.go	0.00% <0.00%> (ø)
x/cronos/keeper/msg_server.go	6.45% <0.00%> (ø)
x/cronos/types/query.pb.gw.go	0.00% <0.00%> (ø)
x/cronos/types/tracer.go	0.00% <0.00%> (ø)
x/cronos/keeper/evm.go	57.62% <66.66%> (+5.90%)	⬆️
x/cronos/keeper/evmhooks.go	80.00% <80.00%> (ø)
x/cronos/keeper/evm_log_handlers.go	86.51% <86.51%> (ø)
x/cronos/keeper/ibc.go	83.06% <100.00%> (+4.88%)	⬆️
... and 9 more

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