Add missing Cargo.lock files and ext/ crate for Rust QL tools test fixtures

[data-douser]

Problem

Several Rust QL tools test directories under server/ql/rust/tools/test/ are missing Cargo.lock files needed for CodeQL database extraction. Additionally, there is no ext/ test crate (with Cargo.toml, Cargo.lock, and empty lib.rs) to serve as a dependency fixture for the Rust test cases.

Without these files, the Rust tools query unit tests may fail to extract test databases or may produce non-deterministic results depending on whether Cargo auto-generates lock files at test time.

Files to add

• server/ql/rust/tools/test/CallGraphFromTo/Cargo.lock
• server/ql/rust/tools/test/CallGraphTo/Cargo.lock
• server/ql/rust/tools/test/PrintCFG/Cargo.lock
• server/ql/rust/tools/test/ext/Cargo.lock
• server/ql/rust/tools/test/ext/Cargo.toml
• server/ql/rust/tools/test/ext/lib.rs

Each Cargo.lock should be a minimal auto-generated lock file for a test package at version 0.0.1. The ext/ crate is an empty library crate (edition = "2021") used as an external dependency fixture.

Context

These files were identified during review of #207 but are unrelated to the Go client rewrite. Splitting them into a dedicated PR to keep changes focused.