feat(l2): add timed prover API

[ilitteri]

Motivation

To measure execution and proving time correctly. This means removing the client initialization from the equation. In the case of ZisK, we use it's own timing exposed via a JSON file generated after proving.

Description

Adds _timed versions for execution and proving for all zkVM backends.

[Copilot]

Pull request overview

This PR adds timed execution and proving capabilities to all zkVM backends by introducing execute_timed and prove_timed functions that measure and return the duration of operations instead of just logging them.

• Adds execute_timed and prove_timed functions to the main prover API and all backend implementations (exec, sp1, risc0, zisk, openvm)
• Removes inline timing/logging from existing execute and prove functions to avoid duplication
• Adds PartialEq derive to the Backend enum for comparison support

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
crates/l2/prover/src/lib.rs	Adds public execute_timed and prove_timed API functions that dispatch to backend-specific implementations
crates/l2/prover/src/backend/exec.rs	Implements execute_timed and prove_timed for the exec backend
crates/l2/prover/src/backend/sp1.rs	Implements execute_timed and prove_timed for SP1, removes timing from non-timed functions
crates/l2/prover/src/backend/risc0.rs	Implements execute_timed and prove_timed for RISC0, removes timing from non-timed functions
crates/l2/prover/src/backend/zisk.rs	Implements execute_timed and prove_timed for ZisK backend
crates/l2/prover/src/backend/openvm.rs	Implements execute_timed and prove_timed for OpenVM backend
crates/l2/prover/src/backend/mod.rs	Adds PartialEq trait to Backend enum
crates/l2/prover/Cargo.toml	Formats the l2 feature definition to single line

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[github-actions]

Lines of code report

Total lines added: 180
Total lines removed: 0
Total lines changed: 180

Detailed view

+-----------------------------------------------+-------+------+
| File                                          | Lines | Diff |
+-----------------------------------------------+-------+------+
| ethrex/crates/l2/prover/src/backend/exec.rs   | 58    | +16  |
+-----------------------------------------------+-------+------+
| ethrex/crates/l2/prover/src/backend/openvm.rs | 79    | +34  |
+-----------------------------------------------+-------+------+
| ethrex/crates/l2/prover/src/backend/risc0.rs  | 130   | +25  |
+-----------------------------------------------+-------+------+
| ethrex/crates/l2/prover/src/backend/sp1.rs    | 153   | +25  |
+-----------------------------------------------+-------+------+
| ethrex/crates/l2/prover/src/backend/zisk.rs   | 138   | +41  |
+-----------------------------------------------+-------+------+
| ethrex/crates/l2/prover/src/lib.rs            | 97    | +39  |
+-----------------------------------------------+-------+------+

[ManuelBilbao]

Unknown fields are ignored by default. We can remove them if we are not going to use them. If we want them for completeness, it's ok then