chore(l2): improve zkVM execution and proving time logs

[ilitteri]

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[Copilot]

Pull Request Overview

This PR improves logging consistency and adds performance timing measurements to the prover backend implementations. The changes standardize logging messages across SP1 and RISC0 backends and modernize string formatting syntax.

• Adds execution time tracking for prove operations in both backends
• Updates log messages to be more descriptive and consistent
• Modernizes string formatting to use inline variable syntax

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
crates/l2/prover/src/backend/sp1.rs	Reorders imports, adds timing for prove operation, updates log messages to include execution duration with modern formatting
crates/l2/prover/src/backend/risc0.rs	Adds timing for prove operation, updates log messages to be more descriptive and include execution duration

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Lines of code report

Total lines added: 4
Total lines removed: 0
Total lines changed: 4

Detailed view

+----------------------------------------------+-------+------+
| File                                         | Lines | Diff |
+----------------------------------------------+-------+------+
| ethrex/crates/l2/prover/src/backend/risc0.rs | 105   | +2   |
+----------------------------------------------+-------+------+
| ethrex/crates/l2/prover/src/backend/sp1.rs   | 128   | +2   |
+----------------------------------------------+-------+------+