docs: fix conf after _build.py changes

`docs/conf.py` tries to read version info from `src/__init__py` using
an expression match. This breaks after e439a0f ("setup.py src/ tests/:
auto-generate pymupdf.pymupdf_version and add git info.", 2025-08-08)
makes `src/__init__py` import that info from `_build.py`, which is
generated during build in the build directory.

Make the build process generate a copy of `_build.py` in `docs` and let
`docs/conf.py` import version info from there.

Alternative fixes:
- pointing `docs/conf.py` at the build directory; this may no longer
  exist after a wheel build, though
- reading from the generated wheel; oh well ;-)
- installing the build and importing `_build.py` from there; this would
  mean intermingling build and install steps

Author: mjg

.gitignore

@@ -4,4 +4,5 @@
 *.swp
 build/
 demo/README.rst
-docs/build
+docs/build
+docs/_build.py

docs/conf.py

@@ -49,16 +49,8 @@
 # built documents.
 #
 # The full version, including alpha/beta/rc tags.
-_path = os.path.abspath(f'{__file__}/../../src/__init__.py')
-with open(_path) as f:
-    for line in f:
-        match = re.search('pymupdf_version = "([0-9][.][0-9]+[.][0-9]+(rc[0-9]+)?)"', line)
-        if match:
-            release = match.group(1)
-            print(f'{__file__}: setting version from {_path}: {release}')
-            break
-    else:
-        raise Exception(f'Failed to find `VersionBind = ...` in {_path}')
+from _build import pymupdf_version as release  # noqa F401
+print(f'{__file__}: setting version from _build.py: {release}')
 
 # The short X.Y version
 version = release

setup.py

@@ -743,6 +743,8 @@ def add(flavour, from_, to_):
     text += f'pymupdf_git_diff = {diff!r}\n'
     text += f'pymupdf_git_branch = {branch!r}\n'
     add('p', text.encode(), f'{to_dir}/_build.py')
+    with open('docs/_build.py', 'w') as f:
+        f.write(text)
 
     # Add single README file.
     if 'p' in PYMUPDF_SETUP_FLAVOUR: