Upgrade ESLint to version 9, Node to 24, and move eslint-plugin-silvermine here

[yokuze]

ADIRL, this PR:

• Upgrades Node to v24 and bumps @silvermine/standardization to the latest
• Upgrades to ESLint 9
  • This involved some rule name changes, which you'll see in the diff
• Moves eslint-plugin-silvermine into this repo, eliminating the cyclical dependency that complicates ESLint upgrades
  • Since this repo contains the plugin also, I moved everything to a src folder and exposed the old paths via package.json's exports field
  • Converted the JS files in the plugin to TS
• Updated testing/code coverage for the plugin to use vitest

Also note that you may see this in the logs when linting now:

[@stylistic/eslint-plugin]: You are using deprecated options("overrides.arrow") in "type-annotation-spacing", please use "arrow-spacing" instead.

This is an intentional choice; it was the lesser of 3 evils:

1. Doing what @Stylistic is suggesting, which results in requiring spacing like: ()=> { instead of () => {
2. Disabling the @stylistic/type-annotation-spacing rule altogether, which lets all kinds of spacing anomalies pass linting
3. Living with the deprecation warning for now until we can figure out another solution