Fix progress bar against non-UTF-8 encodings

For #439.

`file_progress()` sets the progress bar length to the file size in
bytes (`os.path.getsize(file.name)`), but `UpdateWrapper.__iter__`
called `update(len(line))`, which is the decoded character count.
With UTF-16-LE input every character is 2 bytes, so the bar capped
at 50%; UTF-32 capped at 25%; etc.

Simon noted in the issue that the obvious fix (calling `.tell()` on
the wrapped text stream) doesn't work because text mode disables it
during iteration. The underlying binary buffer doesn't have that
restriction though, so this tracks progress against
`TextIOWrapper.buffer.tell()` when the wrapped object exposes one.

For raw binary streams (no `.buffer` attribute) we keep the old
behaviour, which was already byte-accurate.

Added six regression tests in tests/test_utils.py covering UTF-8,
UTF-16-LE, BOM-prefixed UTF-16, the sniff-style `BufferedReader` chain,
a raw binary fallback, and the `.read()` path used by the JSON loader.
Each asserts that the sum of update() calls equals the on-disk file
size, which is what `click.progressbar` needs to reach 100%.

sqlite_utils/utils.py

@@ -210,15 +210,52 @@ class UpdateWrapper:
     def __init__(self, wrapped: io.IOBase, update: Callable[[int], None]) -> None:
         self._wrapped = wrapped
         self._update = update
+        # `file_progress` sets the progress bar length to the file size in
+        # bytes, but iterating a text-mode stream yields decoded characters,
+        # so reporting `len(line)` undercounts for any multi-byte encoding
+        # (UTF-16-LE caps the bar at ~50%, UTF-32 at ~25%, etc.). When the
+        # wrapped object is a text wrapper, track progress against the
+        # underlying binary buffer's position instead. See #439.
+        self._byte_source = getattr(wrapped, "buffer", None)
+        self._last_byte_pos = 0
+        if self._byte_source is not None:
+            try:
+                self._last_byte_pos = self._byte_source.tell()
+            except (io.UnsupportedOperation, OSError):
+                self._byte_source = None
+
+    def _advance_to_buffer_pos(self) -> None:
+        # Bring the progress bar up to the current byte position of the
+        # underlying binary buffer (which may have read ahead).
+        assert self._byte_source is not None
+        try:
+            pos = self._byte_source.tell()
+        except OSError:
+            return
+        delta = pos - self._last_byte_pos
+        if delta > 0:
+            self._update(delta)
+            self._last_byte_pos = pos
 
     def __iter__(self) -> Iterator[bytes]:
+        if self._byte_source is None:
+            for line in self._wrapped:
+                self._update(len(line))
+                yield line
+            return
         for line in self._wrapped:
-            self._update(len(line))
+            self._advance_to_buffer_pos()
             yield line
+        # The wrapper may have buffered the last chunk without emitting any
+        # more lines; flush the remaining bytes so the bar reaches 100%.
+        self._advance_to_buffer_pos()
 
     def read(self, size: int = -1) -> bytes:
         data = self._wrapped.read(size)
-        self._update(len(data))
+        if self._byte_source is not None:
+            self._advance_to_buffer_pos()
+        else:
+            self._update(len(data))
         return data