chore(nix): relock logos-module-builder onto the crates.io CDN wiring

[igor-sirotin]

Description

1. Relocked logos-module-builder in both module flakes and in the root flake, 6ef42ea (Jul 1) → 9f420c2 (Sep 8). That rev carries fix(nix): apply logos-nix's native overlays in mkPkgsWith logos-module-builder#233 and #234, which apply logos-nix's lib.nativeOverlays across the closure — so every crate now comes from static.crates.io instead of the /api/v1 endpoint crates.io 403s.
2. Relocked rust-lib's Cargo.lock onto logos-rust-sdk 0.3.0, the path-dep version the module-builder bump moves.
3. Dropped the CI crate-prefetch step, whose own comment said to remove it once the module-builder pin fetched from the CDN itself.

Crate fetches on the dead endpoint, counted over .#logos-rln-module-lgx and .#logos-lez-rln-module-lgx: 0 of 321 and 0 of 403. Every root output except wallet-module builds.

AI-made decisions

• The root flake.lock pins its own copy of each path input's graph, so bumping the two sub-flake locks alone left nix build .#... at the root still resolving module-builder 6ef42ea. Both sub-flake locks and the root lock have to move together; CI never caught it because both jobs build path:./logos-rln-module, never the root flake.
• Removed the prefetch step in the same PR rather than a follow-up: leaving it would let CI pass without ever exercising the fetch path this bump changes.
• Kept each concern as its own commit, so any of them can be dropped without losing the others.
• logos-execution-zone stays deliberately pinned to the v0.2.2-era rev, so wallet-module is untouched and still fails: 161 of its 1122 crate fetches remain on the dead endpoint, all inside a closure that is not a logos-nix consumer and so out of reach of this change.