Fix grammar in comments and documentation

[Marcofann]

This pull request corrects grammatical errors in comments and documentation files across multiple modules. Specifically, it replaces instances of "a" with "an" where appropriate (e.g., before words starting with a vowel sound). The changes improve the readability and professionalism of the codebase.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Contents

This PR contains:

• Fixed grammar in comments and documentation:
  • Replaced "a evm" with "an evm" in tests.rs.
  • Replaced "an new instance" with "a new instance" in storage.rs and transient_storage.rs.
  • Replaced "a Ethereum block" with "an Ethereum block" in geth_types.rs.
  • Replaced "a RPC node" with "an RPC node" in readme.md.