feat(nix): bump nixpkgs & use verilator 5.042 with optimization patch

[ngc7331]

Overrides to verilator:

• dropped patches (fix: fix V3Hash MacOS ambiguity again verilator/verilator#6350) from nixpkgs as it's included in verilator 5.042
• add patch Optimize mux with UInt To OneHot (#6760) verilator/verilator#6822

This should have some benefit in improving simulation speed

[Copilot]

Pull request overview

This PR updates the Nix development environment by bumping nixpkgs from version 25.05 to 25.11 and upgrading Verilator from version 5.040 to 5.042 with an optimization patch to improve simulation performance.

• Upgrades nixpkgs to nixos-25.11
• Updates Verilator to version 5.042 with new source hash
• Replaces nixpkgs upstream patches with a performance optimization patch from PR #6822

Reviewed changes

Copilot reviewed 1 out of 2 changed files in this pull request and generated 1 comment.

File	Description
flake.nix	Updates nixpkgs reference to 25.11, upgrades Verilator to 5.042, and applies optimization patch for improved mux performance
flake.lock	Updates lock file to reflect nixpkgs 25.11 with corresponding revision and hash updates

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[cyyself]

Is it already replaced by #71?

[ngc7331]

Is it already replaced by #71?

@cyyself Probably yes. We're waiting for server upgrading to 24.04 (maybe this weekend?), after that we can merge #71 and deploy verilator5.044 & clang19 & openjdk21. Otherwise we still need this as a temp solution.