support Vite's base config when using the dev server

[DeedleFake]

• Quick Checklist

• I have read the contributing guidelines
• I have written new tests, as applicable (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• I have added a changeset, if applicable

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

It adds support for Vite's base config in the dev server. This fixes issues with serving assets through imagetools when using a custom backend, such as Rails.

Fixes #396.

• What is the new behavior (if this is a feature change)?

The URL prefix used to watch for imagetools requests is now ${viteConfig.base}/@imagetools/ instead of just /@imagetools/. This allows for things like Rails to properly forward those requests to the Vite dev server.

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this
  PR?)

I don't think so, no.

[changeset-bot]

🦋 Changeset detected

Latest commit: a0f8876

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
vite-imagetools	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[codecov]

Codecov Report

Merging #489 (479afe7) into main (c64e7ef) will increase coverage by 0.00%.
The diff coverage is 40.00%.

❗ Current head 479afe7 differs from pull request most recent head a0f8876. Consider uploading reports for the commit a0f8876 to get more accurate results

@@           Coverage Diff           @@
##             main     #489   +/-   ##
=======================================
  Coverage   96.74%   96.75%           
=======================================
  Files          31       31           
  Lines        1107     1109    +2     
  Branches      222      222           
=======================================
+ Hits         1071     1073    +2     
  Misses         36       36           

Flag	Coverage Δ
imagetools-core	98.68% <ø> (ø)
rollup-plugin-imagetools	99.23% <ø> (ø)
vite-imagetools	83.33% <40.00%> (+0.23%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
packages/vite/src/index.ts	83.33% <40.00%> (+0.23%)	⬆️

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[DeedleFake]

Is there anything else you'd like me to do before this can be merged? My current workaround involves manually building vite-imagetools and then repackaging as a minimal local package so that I can use the fixed version, and I'd very much prefer to be able to use the actual package itself.