feat: Match more class declarations for export alias check

[AbhiPrasad]

In #29 I added support for export alias matching, allowing for orchestrion to instrument minified classes/functions as long as they were exported with a proper name.

This PR matches more class declarations for the export alias check, which was needed for the @google/adk instrumentation.

AI Summary

Key changes in src/instrumentation.rs:

1. Support for var/let/const class expressions — When a class is assigned to a variable (e.g., var X = class { ... } or var X = class Y { ... }), the instrumentor now propagates the variable name to the class expression so it can be matched for tracing. For named class expressions (class Y), it sets is_correct_class directly using the variable name instead.

2. Support for assignment-based class expressions — Same logic extended to assignment expressions like X = class { ... }.

3. Prevent overriding is_correct_class in visit_mut_class_expr — If is_correct_class was already set by visit_mut_var_decl (for var X = class Y {} patterns), visit_mut_class_expr no longer overwrites it.

Tests added:

4 new test cases covering const, let, var, and named-class-in-var export alias patterns (each with mod.mjs, mod.rs, and test.mjs files).

[timfish]

Looks good!

There are a couple of clippy format/style failures in CI.