Refactor compression flow with routing seam

Introduce compress_image_with_routing and compress_raster_image to prepare extensible backend routing while keeping existing behavior unchanged.

Add unit test that verifies routing currently delegates to raster compressor.

Co-Authored-By: Abacus.AI CLI <agent@abacus.ai>

pptx_image_compress.py

@@ -218,6 +218,42 @@ def run_compressor(
     return compressor(original, out_dir, caesium_threads, quality, min_savings)
 
 
+def compress_raster_image(
+    compressor: Callable[..., Path | None],
+    original: Path,
+    out_dir: Path,
+    caesium_threads: int | None,
+    quality: int,
+    min_savings: str,
+) -> Path | None:
+    return run_compressor(
+        compressor=compressor,
+        original=original,
+        out_dir=out_dir,
+        caesium_threads=caesium_threads,
+        quality=quality,
+        min_savings=min_savings,
+    )
+
+
+def compress_image_with_routing(
+    compressor: Callable[..., Path | None],
+    original: Path,
+    out_dir: Path,
+    caesium_threads: int | None,
+    quality: int,
+    min_savings: str,
+) -> Path | None:
+    return compress_raster_image(
+        compressor=compressor,
+        original=original,
+        out_dir=out_dir,
+        caesium_threads=caesium_threads,
+        quality=quality,
+        min_savings=min_savings,
+    )
+
+
 def update_relationship_targets(work_dir: Path, old_name: str, new_name: str) -> None:
     rels_namespace = "{http://schemas.openxmlformats.org/package/2006/relationships}Relationship"
     for rels_file in work_dir.rglob("*.rels"):
@@ -321,7 +357,7 @@ def process_image_file(
 
     try:
         out_sub = scratch_dir / f"img_{idx:06d}"
-        caesium_out = run_compressor(
+        caesium_out = compress_image_with_routing(
             compressor=compressor,
             original=img_path,
             out_dir=out_sub,