fix: resolve 8 integration test compilation errors (#46)

## Problem
8 integration test files failed to compile due to:
1. Ambiguous float types (Rust 2024+ stricter inference)
2. chrono 0.4 API change (`with_hour` removed)
3. Missing `sqlx` + `base64` in `[dev-dependencies]`
4. `<` parsed as generics instead of comparison
5. Incorrect assertion (3^5=243 > 100)

## Fix
- Added `f32`/`f64` type annotations to vec declarations and bindings
- Replaced `with_hour(0)` with `date_naive().and_hms_opt(0,0,0).unwrap().and_utc()`
- Added `sqlx` + `base64` to `[dev-dependencies]`
- Wrapped comparison in parens
- Fixed assertion: nodes=100 → nodes=1000

## Validation
- `cargo build --release` clean
- `cargo test` — 20 test suites, 0 failures
- 10 files changed, 46 insertions, 42 deletionsReviewed-on: #46

Co-authored-by: rock <[email protected]>

crates/mem-core/tests/it_m3_8_gate.rs

@@ -103,7 +103,7 @@ fn gate_metadata_preservation() {
 
     // Verify we get a valid OptimizedChunk with proper fields
     assert!(optimized.original_tokens > 0, "should track original tokens");
-    assert!(optimized.compressed_tokens >= 0, "should track compressed tokens");
+    assert!(optimized.compressed_tokens <= optimized.original_tokens, "compressed should not exceed original");
 }
 
 #[test]
@@ -122,7 +122,7 @@ fn gate_error_handling_graceful() {
         match optimizer.optimize(case.as_str()) {
             Ok(result) => {
                 // Valid compression
-                assert!(result.original_tokens >= 0);
+                assert!(result.original_tokens > 0);
             }
             Err(_) => {
                 // Acceptable to fail on edge cases, but should fail gracefully
@@ -209,7 +209,7 @@ fn gate_no_regressions_existing_functionality() {
 
     assert!(!result.compressed.is_empty(), "basic optimization should work");
     assert!(result.original_tokens > 0, "should track tokens");
-    assert!(result.compressed_tokens >= 0, "should have compressed tokens");
+    assert!(result.compressed_tokens <= result.original_tokens, "compressed should not exceed original");
 }
 
 // ============================================================================