fix: charge the budget for compressed tar bytes that are skipped, not just kept

The tree decompression budget was only spent as entry content was stored. A compressed tar reader
still decompresses whatever an entry leaves unread to reach the next header, so an excluded entry, a
file/directory clash, or the rest of one over the 2 GB per-entry cap decompressed with nothing charged
and no ctx check. A small `.tar.zst` could force hundreds of GB of work past the budget.

- in compressed tars the rest of every regular entry is now drained through the budget, with ctx
  checked per chunk
- zip and plain tar are unchanged: they seek past skipped entries, so those cost nothing

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

internal/archive/extract.go

@@ -139,14 +139,21 @@ func (r *Resolver) extract(ctx context.Context, format archives.Extractor, conte
 	if _, err := content.Seek(0, io.SeekStart); err != nil {
 		return err
 	}
+	// a compressed tar decompresses whatever an entry leaves unread to reach the next header, so there the
+	// bytes of skipped entries cost as much as kept ones. A zip or a plain tar seeks past them for free
+	_, drains := format.(archives.CompressedArchive)
 	err := format.Extract(ctx, content, func(_ context.Context, f archives.FileInfo) error {
 		hdr, ok := r.entryHeader(f)
-		if !ok || exclusions.Excludes(hdr.Name) {
-			return nil
-		}
+		skip := !ok || exclusions.Excludes(hdr.Name)
 		if !f.Mode().IsRegular() {
+			if skip {
+				return nil
+			}
 			return r.add(hdr, nil)
 		}
+		if skip && !drains {
+			return nil
+		}
 		entry, err := f.Open()
 		if err != nil {
 			log.WithFields("entry", hdr.Name, "error", err).Trace("unable to open archive entry, skipping it")
@@ -157,7 +164,16 @@ func (r *Resolver) extract(ctx context.Context, format archives.Extractor, conte
 				log.WithFields("entry", hdr.Name, "error", err).Trace("unable to close archive entry")
 			}
 		}()
-		return r.add(hdr, entry)
+		if !skip {
+			if err := r.add(hdr, entry); err != nil {
+				return err
+			}
+		}
+		if !drains {
+			return nil
+		}
+		// what add left unread (the rest of an entry over the size cap, or one skipped whole) is charged here
+		return r.drain(ctx, entry)
 	})
 	r.finish()
 	if errors.Is(err, ErrDiskLimitReached) {