fix: capture instantiateVariableFont return value (#1911)

instantiateVariableFont() returns a *new* TTFont with the requested axes
pinned; the existing call discards that return and proceeds to
font.save() the original (still-variable) font. The "static instance"
written to disk is therefore identical to the source variable font and
the requested axis values are silently ignored.

For sd-fonts.yaml entries that use the `variable: {wght: 400}` form
(e.g. Bitter, Lora) this means every weight ends up rasterised from the
same default-weight glyphs — bold and regular look the same.

Capture the return value, and pass two diagnostically useful kwargs
while we're touching the call:

* updateFontNames=True — rewrite the name table so the saved TTF reports
its actual weight/style instead of retaining the source variable-font
names.
* optimize=False        — skip the gvar interpolation optimisation;
                          fully pinning every axis drops gvar anyway,
                          so the work would be wasted.

The atomic-write scaffolding around the call is left untouched.

## Summary

* **What is the goal of this PR?** (e.g., Implements the new feature for
file uploading.)
* **What changes are included?**

## Additional Context

* Add any other information that might be helpful for the reviewer
(e.g., performance implications, potential risks,
  specific areas to focus on).

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lib/EpdFont/scripts/build-sd-fonts.py

@@ -85,15 +85,29 @@ def extract_static_instance(source_path: Path, axes: dict, family_name: str, sty
     tmp_fd, tmp_name = tempfile.mkstemp(suffix=".ttf", dir=cached.parent)
     os.close(tmp_fd)
     tmp_path = Path(tmp_name)
-    font = TTFont(str(source_path))
+    # Keep separate handles for the source variable font and the static
+    # instance: instantiateVariableFont with default inplace=False returns a
+    # *new* TTFont, so rebinding `font` would otherwise strand the source's
+    # file handle open until GC runs.
+    #
+    # updateFontNames=True   — rewrite the name table so the saved font
+    #                          reports its weight/style accurately rather
+    #                          than retaining the variable-font names.
+    # optimize=False         — skip the gvar interpolation optimisation;
+    #                          fully pinning every axis drops gvar anyway,
+    #                          so the work would be wasted.
+    source_font = TTFont(str(source_path))
     try:
-        instantiateVariableFont(font, axes)
-        font.save(str(tmp_path))
+        font = instantiateVariableFont(source_font, axes, updateFontNames=True, optimize=False)
+        try:
+            font.save(str(tmp_path))
+        finally:
+            font.close()
     except Exception:
         tmp_path.unlink(missing_ok=True)
         raise
     finally:
-        font.close()
+        source_font.close()
     tmp_path.replace(cached)
 
     return cached