chore(deps): bump vecq-core to 0.3.0

[ajianaz]

What

vecq-core 0.3.0 is live on crates.io. Root Cargo.toml line 75 still pins vecq-core = "0.2.0".

What 0.3.0 brings

Keyed API (u64-key insert/replace/tombstone/relabel), Matryoshka working_dim, cascade search (2-bit prefilter + 4-bit rescore), residual mode, configurable width (set_bits(4|5|6)), zero-copy VecqView (mmap serving, ~64 µs vs ~4.9 ms at 12k vectors), x86_64 AVX2 path.

https://github.com/codecoradev/vecq/releases/tag/v0.3.0

⚠️ Behavior change to review when bumping

• VecqIndex::new now defaults to 5-bit width (was 4-bit). Storage ~+19%/vector, recall up (4.78x compression, recall@10 0.979 on real 768-dim data). Call set_bits(4) where the old profile is required.
• File formats v1.2–v1.5: new 0.3.0-written files are NOT readable by 0.1/0.2 readers; 0.3.0 reads all old files (v1–v1.5).

Why

Pick up the mmap view (serving without RAM load), keyed ops, and the 5-bit recall profile; stay on a current dependency.

Acceptance

• Bump vecq-core to 0.3 in root Cargo.toml, cargo update -w
• Decide per call-site: accept new 5-bit default or pin set_bits(4) explicitly
• CI green