Rust: add proc-macro capabilities to QL tests

[redsun82]

This adds the possibility to add a special proc_macro.rs source file to QL tests, which will be generated into a proc_macro crate the usual lib crate depends on.

This allow to define procedural macros in QL tests, and is here used to move the macro-expansion integration test to be a language test instead.

As the generated manifests involved were starting to get a bit complex, they are now generated from a mustache template.

The path resolution inconsistency might have to do with using a .. path for the crate sources, might be worth investigating in a follow-up.

[Copilot]

Pull Request Overview

This PR extends QL tests with procedural macro support by generating a separate proc_macro crate for test macros and migrating the macro-expansion extractor tests to use this new setup. It introduces a Mustache-based template for Cargo manifest generation and updates the extractor harness accordingly.

• Replace custom Cargo manifest code with a Mustache template and TestCargoManifest in qltest.rs.
• Add proc_macro.rs, new test code (macro_expansion.rs, call.rs), and updated QL tests/expected outputs under extractor-tests/macro-expansion.
• Remove legacy underscore-named tests and integration Python test, update Bazel build files to include the Mustache template.

Reviewed Changes

Copilot reviewed 27 out of 33 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
rust/ql/test/extractor-tests/macro_expansion/test.ql	Removed old underscore-named QL test
rust/ql/test/extractor-tests/macro_expansion/*.expected, options.yml, macro_expansion.rs	Removed legacy extractor tests
rust/ql/test/extractor-tests/macro-expansion/test.ql	Added new QL test with Diagnostics import and warnings predicate
rust/ql/test/extractor-tests/macro-expansion/test.expected	New expected output for macro-expansion test
rust/ql/test/extractor-tests/macro-expansion/proc_macro.rs	Added procedural macro definitions (add_one, erase)
rust/ql/test/extractor-tests/macro-expansion/macro_expansion.rs	New Rust code exercising attribute and function-like macros
rust/ql/test/extractor-tests/macro-expansion/call.rs	Test harness calls expanded functions
rust/ql/test/extractor-tests/macro-expansion/CONSISTENCY/PathResolutionConsistency.expected	Added path-resolution consistency test
rust/ql/test/.gitignore	Ignore generated .proc_macro/ and .lib/ directories
rust/ql/integration-tests/macro-expansion/*	Removed old Python integration test and expected outputs
rust/extractor/src/qltest_cargo.mustache	New Mustache template for Cargo.toml generation
rust/extractor/src/qltest.rs	Introduce TestCargoManifest and replace manifest logic
rust/extractor/Cargo.toml	Added mustache = "0.9.0" dependency
rust/extractor/BUILD.bazel	Include Mustache template in build inputs
misc/bazel/3rdparty/tree_sitter_extractors_deps/defs.bzl	Add mustache to Bazel external dependencies

[aibaars]

LGTM , thanks!