feat: extract minimal chekov-core state model

[Freyskeyd]

Summary

• Add dependency-free chekov-core with opaque byte keys and values, revisions, cells, views, mutations, observations, and transition batches.
• Add deterministic memory-backed tests for creation, update, deletion, stale observations, transition construction, and revision exhaustion.
• Refs CHE-3.

Verification

• cargo test --workspace
• cargo clippy -p chekov-core --all-targets -- -D warnings
• cargo fmt --all -- --check

[linear-code]

CHE-3

[Copilot]

🟡 Changes recommended

From<Vec<u8>> for StateKey/StateValue currently performs an avoidable extra allocation+copy, which conflicts with the “cheaply shareable” intent and is straightforward to fix.

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Pull request overview

This PR introduces a new dependency-free chekov-core crate that defines a minimal, domain-neutral state model (opaque byte keys/values, revisions, observations, mutations, and transition batches) intended for deterministic execution in the broader Chekov codebase.

Changes:

• Added chekov-core with core state types (StateKey, StateValue, Revision, StateCell, Mutation, TransitionBatch) and a StateView trait.
• Added deterministic memory-backed tests covering create/update/delete, stale revisions, transition batching, and revision exhaustion.
• Registered the new crate in workspace lockfile.

File summaries

File	Description
crates/chekov-core/src/lib.rs	Implements the minimal state model API plus memory-backed tests.
crates/chekov-core/Cargo.toml	Declares the new chekov-core crate metadata as workspace-managed.
Cargo.lock	Adds the new chekov-core package entry to the lockfile.

Review details

Suppressed comments (1)

crates/chekov-core/src/lib.rs:108

• From<Vec<u8>> currently calls StateValue::new(bytes), which copies via AsRef<[u8]>. You can preserve the “cheaply shareable” goal by converting Vec<u8> directly into Arc<[u8]> to avoid an extra allocation+memcpy.

impl From<Vec<u8>> for StateValue {
    fn from(bytes: Vec<u8>) -> Self {
        Self::new(bytes)
    }
}

• Files reviewed: 2/3 changed files
• Comments generated: 1
• Review effort level: Lite

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[Freyskeyd]

Fixed in b4394d7. Both Vec conversions now construct Arc<[u8]> directly, avoiding the extra copy. Workspace tests, clippy, and formatting checks pass.