fix: support multiple plugin instances using the transform option

[mattlewis92]

When using multiple instances of the plugin and the transform option, the plugin fails with an error like so:

ERROR: Do not know how to load path: esbuild-sass-plugin:css-chunk:test/fixture/multiple/src/modules/example.module.scss

This is due to the namespace and css chunk prefix being shared between all plugin instances. We fix the bug by adding a simple unique incrementing id to the namespace and css prefix used by the plugin.