fix: remove unused dat macro imports

[seriouscoderone]

Summary

• Remove redundant dat macro imports that cause compilation failures
• Modernize GitHub Actions CI workflow
• The dat! macro is already available crate-wide via #[macro_use] on the data module

Bug Fix

The project currently fails to compile because of unused import warnings treated as errors:

error: unused import: `dat`
 --> src/core/common.rs:1:19
  |
1 | use crate::data::{dat, Value};
  |                   ^^^

Since lib.rs declares #[macro_use] pub mod data;, the dat! macro is automatically available throughout the crate without explicit imports.

CI Improvements

• Replace deprecated actions-rs/toolchain with dtolnay/rust-toolchain
• Update actions/checkout to v4
• Add cargo caching for faster builds
• Split into parallel jobs (check, audit, wasm)
• Properly install cargo-audit before running security audit

Files Changed

Bug fix:

• src/core/common.rs - module and test
• src/core/creder.rs
• src/core/pather.rs - test
• src/core/prefixer.rs - test
• src/core/sadder.rs - test
• src/core/saider.rs - module and test
• src/core/serder.rs
• src/core/tholder.rs
• src/data.rs - test

CI:

• .github/workflows/test.yml

Test plan

• cargo test passes (832 tests)
• cargo build succeeds
• Doc tests pass
• CI workflow will run on this PR

🤖 Generated with Claude Code