fix typos

[Marcofann]

This pull request addresses grammatical errors in documentation comments across multiple files in the repository. The changes improve the readability and accuracy of the comments, ensuring a more polished codebase.

Files Updated

1. gas_oracle.rs

   • Corrected "a enum" to "an enum."

2. runner.rs

   • Corrected "a RPC server" to "an RPC server."

3. token.rs

   • Corrected "to a hash function" to "to an hash function."