fix: make row publication concurrency-safe by default - #45

Closes #37
Closes #40

Summary

• make immutable row-version publication mandatory for generated safe APIs, including no-default-feature builds
• retain the former versioned-row-publication feature name as a compatibility no-op
• revalidate generated point and range reads against current index mappings and defer link/page reuse until active readers drain
• make delete return NotFound rather than panic in the staged insert publication window, with deterministic regression coverage
• serialize Congee mutations because congee-wt 0.4.1 can lose disjoint structural insert/remove updates; native concurrent point reads remain unchanged

Verification

• cargo fmt --all -- --check
• cargo clippy --all-targets -- -D warnings
• cargo test
• cargo clippy --all-targets --no-default-features -- -D warnings
• cargo test --no-default-features
• cargo check --all-targets --features versioned-row-publication
• Congee immediate disjoint insert/read/remove test: 100 consecutive focused passes