Refactor end-to-end tests: Move e2e tests from zkvm/prover.rs to a dedicated e2e_tests.rs file

[moodlezoup]

Currently, the end-to-end tests in zkvm/prover.rs are starting to clutter the file. To improve maintainability and enable more comprehensive test sweeps (for example, across different DoryLayout enum variants and other configs), these e2e tests should be separated into a new e2e_tests.rs file or similar.

Action Items:

• Move e2e and integration-heavy tests out of zkvm/prover.rs into a new test file (e.g., e2e_tests.rs or within a tests/ directory, as appropriate).
• Consider instrumenting these tests to allow easy parameterization/sweeps over Dory layout enum and other configuration options.
• Ensure developer ergonomics for running both unit and e2e tests separately or together.

This will make the codebase cleaner and set up for more flexible test coverage.