ci: initialize rust ci

[fbac]

Closes https://github.com/zeta-chain/protocol-contracts-solana/issues/8

Introduces:

• CODEOWNERS file.
• Formatting script leveraging cargo fmt.
  • Discussion: current script uses brew to install rustfmt. We could be using rustup too, the script should check whether brew or rustup are available on the host.
• .gitignore with all the current paths needed to ignore.
• Check workflow: format, clippy, doc and hack. Based on the standard set by OpenZeppelin.
• Coverage workflow.
• nostd workflow: code should be able to run without rust std.
• Test workflow.

[lumtis]

Added the CODECOV_TOKEN

[codecov-commenter]

Welcome to Codecov :tada:

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