fix: label count params should be c_int in the pub extern "C" fn init_unified_classifier_c

[carlory]

What type of PR is this?

fix: label count params should be c_int in the pub extern "C" fn init_unified_classifier_c

What this PR does / why we need it:

unified_classifier.go:
// C function declarations - Legacy low confidence functions
bool init_unified_classifier_c(const char* modernbert_path, const char* intent_head_path,
                               const char* pii_head_path, const char* security_head_path,
                               const char** intent_labels, int intent_labels_count,
                               const char** pii_labels, int pii_labels_count,
                               const char** security_labels, int security_labels_count,
                               bool use_cpu);

lib.rs:
/// Initialize unified classifier (called from Go)
#[no_mangle]
pub extern "C" fn init_unified_classifier_c(
    modernbert_path: *const c_char,
    intent_head_path: *const c_char,
    pii_head_path: *const c_char,
    security_head_path: *const c_char,
    intent_labels: *const *const c_char,
    intent_labels_count: usize,
    pii_labels: *const *const c_char,
    pii_labels_count: usize,
    security_labels: *const *const c_char,
    security_labels_count: usize,
    use_cpu: bool,
) -> bool {

DEBUG log:

DEBUG: security_labels ptr = 0x140000455d0, count = 4294967298

root cause:

4294967298 = 0x100000002 = 2^32 + 2
The Rust function signature uses usize (64 bits), but Go passes C.int (32 bits).

test with this patch:

(base) ➜  semantic-router git:(fix-unit-test) make build
==================> Running rust ============> ...
Building Rust library...
   Compiling candle-semantic-router v0.4.0 (/Users/kiki/workspace/semantic-router/candle-binding)
    Finished `release` profile [optimized] target(s) in 3.99s
==================> Running build-router ============> ...
# command-line-arguments
ld: warning: ignoring duplicate libraries: '-lcandle_semantic_router'
(base) ➜  semantic-router git:(fix-unit-test) src/semantic-router/pkg/utils/classification
(base) ➜  classification git:(fix-unit-test) go test -timeout 300s -count=1 --run ^TestUnifiedClassifier_Initialize$/^Initialization_attempt$ github.com/vllm-project/semantic-router/src/semantic-router/pkg/utils/classification
# github.com/vllm-project/semantic-router/src/semantic-router/pkg/utils/classification.test
ld: warning: ignoring duplicate libraries: '-lcandle_semantic_router'
ok  	github.com/vllm-project/semantic-router/src/semantic-router/pkg/utils/classification	0.836s

Which issue(s) this PR fixes:

Fixes #481

Release Notes: Yes/No

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[github-actions]

👥 vLLM Semantic Team Notification

The following members have been identified for the changed files in this PR and have been automatically assigned:

📁 candle-binding

Owners: @rootfs
Files changed:

• candle-binding/src/lib.rs

---

🎉 Thanks for your contributions!

This comment was automatically generated based on the OWNER files in the repository.

[rootfs]

@carlory we are trying to refactor the candle binding in #207

Can you create the PR against the feat-candle-refactoring branch? Thanks

[carlory]

@rootfs recreated #494
/close