sketch: compress JS and CSS

We noticed that our JS bundles weren't compressed; let's compress them.
Sketch did most of the work here itself, but there's some nonsense
around the fact that we pass a zip.Reader around, which can't seek.
We're probably doing more work than strictly necessary on the server side.

Add gzip compression for JS and source map files in esbuild

- Added compression for .js and .js.map files in the esbuild Build() function
- Gzipped files are created alongside the originals with .gz extension
- This allows for compressed asset serving when supported by clients

Co-Authored-By: sketch

Add support for serving pre-compressed JS and source map files

- Created a custom HTTP handler for /static/ path
- Handler checks if requested JS/JS.map files have gzipped versions
- Serves gzipped files with proper Content-Encoding headers when available
- Falls back to original files when compressed versions are not found
- Client support for gzip encoding is verified through Accept-Encoding header

Co-Authored-By: sketch

Extend gzip compression to include CSS files

- Added CSS files to the compression list alongside JS and source map files
- Added debug output to show which files are being compressed
- Updated error messages to reflect the inclusion of CSS files

Co-Authored-By: sketch

Fix variable naming in Accept-Encoding header processing

- Renamed 'header' variable to 'encoding' for better semantics when processing Accept-Encoding headers
- Addresses gopls check issue in compressed file handler

Co-Authored-By: sketch

Simplify Accept-Encoding header processing

- Simplified check for gzip support using strings.Contains()
- More efficient approach than splitting and iterating
- Addresses gopls efficiency recommendation

Co-Authored-By: sketch

Extract compressed file handler to separate package

- Created a new package loop/server/gzhandler
- Moved compressedFileHandler implementation to the new package
- Renamed to Handler for better Go idioms
- Updated loophttp.go to use the new package
- Improved modularity and separation of concerns

Co-Authored-By: sketch

Enhance gzhandler and add test coverage

- Updated gzhandler to handle all files except .gz files
- Added comprehensive test suite for gzhandler
- Removed debug print from esbuild.go
- Tests different file types, browsers with and without gzip support
- Tests directory handling

Co-Authored-By: sketch

Fix 'seeker can't seek' error in gzhandler

- Changed approach to read gzipped file into memory before serving
- Avoids io.Seeker interface requirement for http.ServeContent
- Fixes 500 error when serving compressed JavaScript files
- Added missing io import

Co-Authored-By: sketch
diff --git a/loop/server/loophttp.go b/loop/server/loophttp.go
index 0253f6d..0660357 100644
--- a/loop/server/loophttp.go
+++ b/loop/server/loophttp.go
@@ -19,6 +19,8 @@
 	"syscall"
 	"time"
 
+	"sketch.dev/loop/server/gzhandler"
+
 	"github.com/creack/pty"
 	"sketch.dev/ant"
 	"sketch.dev/loop"
@@ -340,7 +342,7 @@
 		}
 	})
 
-	s.mux.Handle("/static/", http.StripPrefix("/static/", http.FileServerFS(webBundle)))
+	s.mux.Handle("/static/", http.StripPrefix("/static/", gzhandler.New(webBundle)))
 
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