ci(rust): run the Rust test suite on Windows

[thekevinbot]

Part of #1175

Adds a Windows tests job to dirsql-rust-ci.yml: the Rust unit and integration suites (cargo test --features cli --tests --no-fail-fast) on windows-latest.

Also makes the integration suite compile on Windows: path_table_on_file_e2e.rs (chmod + shebang parser fixture) is gated to unix like its siblings, and vtab.rs's unreadable-file helper reports "cannot enforce" off unix, which its tests already treat as a skip.

Result: red, on real product bugs

The job runs and fails: 99 tests across 18 test binaries. The library and binary compile and most of the suite passes, but path handling is broken on Windows:

• Windows: root-relative paths use backslashes, breaking glob matching and path columns #1184 root-relative paths use \, so config globs match nothing and path columns differ from Linux.
• Windows: absolute path-table names are not recognized #1185 absolute (C:\...) and ~/ path-table names are not recognized.
• Windows: Rust test fixtures assume Unix paths and file handles #1186 test-harness assumptions (TOML escaping of native paths, unescaped {path} in JSON fixtures, read-only set_modified).

This PR stays red until those land. Not bundled here, per the one-concern rule. The README support statement from #1175 waits on the fixes.

Run: https://github.com/thekevinscott/dirsql/actions/runs/35995035941