docs(l2): add timelock contract docs

[JereSalo]

Motivation

Description

Add docs for the Timelock.sol contract

[github-actions]

Lines of code report

Total lines added: 28
Total lines removed: 9
Total lines changed: 37

Detailed view

+--------------------------------------------+-------+------+
| File                                       | Lines | Diff |
+--------------------------------------------+-------+------+
| ethrex/cmd/ethrex/build_l2.rs              | 447   | +5   |
+--------------------------------------------+-------+------+
| ethrex/cmd/ethrex/l2/command.rs            | 647   | +2   |
+--------------------------------------------+-------+------+
| ethrex/cmd/ethrex/l2/deployer.rs           | 1481  | -9   |
+--------------------------------------------+-------+------+
| ethrex/cmd/ethrex/l2/options.rs            | 1072  | +10  |
+--------------------------------------------+-------+------+
| ethrex/crates/l2/sequencer/configs.rs      | 107   | +1   |
+--------------------------------------------+-------+------+
| ethrex/crates/l2/sequencer/l1_committer.rs | 1384  | +10  |
+--------------------------------------------+-------+------+

[Copilot]

Pull request overview

This PR adds comprehensive documentation for the Timelock.sol contract, which serves as an access control layer for the OnChainProposer contract by managing role-based permissions and scheduled operations with delays.

Key Changes

• Introduces documentation explaining the Timelock contract's role architecture (Sequencers, Governance, and Security Council)
• Documents core functionalities including scheduling, executing, and canceling operations
• Provides guidance on operation ID collision handling and cancellation procedures

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[ManuelBilbao]

Just a few nit comments