feat: add custom logits processors and native diagnostics

[zatevakhin]

summary

• add panic-contained custom logits processors with safe blocking, streaming, and asynchronous lifetime and error handling
• expose linked native version diagnostics and document the current zero-priority scheduler behavior
• replace the legacy test-model downloader with the pinned Hugging Face resolver while keeping ordinary tests network-free

validation

• formatting, clippy, model-free offline tests, docs, exact Rust 1.85.0 checks, package checks, and independent review pass
• resolver tests and setup-example compile checks pass
• online model acquisition, model-backed Qwen tests, sanitizers, and TSan were not run