Rewrite Python binding with C extension

python/_lc3.pyi

@@ -0,0 +1,87 @@
+#
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+import collections.abc
+
+class EncoderContext:
+    def __init__(
+        self,
+        hrmode: bool,
+        dt_us: int,
+        sr_hz: int,
+        sr_pcm_hz: int,
+        nchannels: int,
+    ) -> None: ...
+    def encode(
+        self,
+        pcm: collections.abc.Buffer,
+        num_bytes: int,
+        pcm_format: int,
+    ) -> bytes: ...
+    def disable_ltpf(self) -> None: ...
+
+class DecoderContext:
+    def __init__(
+        self,
+        hrmode: bool,
+        dt_us: int,
+        sr_hz: int,
+        sr_pcm_hz: int,
+        nchannels: int,
+    ) -> None: ...
+    def decode(
+        self,
+        data: collections.abc.Buffer | None,
+        pcm_format: int,
+    ) -> bytes: ...
+
+def hr_frame_samples(
+    hrmode: bool,
+    dt_us: int,
+    sr_hz: int,
+) -> int: ...
+
+def hr_frame_block_bytes(
+    hrmode: bool,
+    dt_us: int,
+    sr_hz: int,
+    nchannels: int,
+    bitrate: int,
+) -> int: ...
+
+def hr_resolve_bitrate(
+    hrmode: bool,
+    dt_us: int,
+    sr_hz: int,
+    nbytes: int,
+) -> int: ...
+
+def hr_delay_samples(
+    hrmode: bool,
+    dt_us: int,
+    sr_hz: int,
+) -> int: ...
+
+def hr_encoder_size(
+    hrmode: bool,
+    dt_us: int,
+    sr_hz: int,
+) -> int: ...
+
+def hr_decoder_size(
+    hrmode: bool,
+    dt_us: int,
+    sr_hz: int,
+) -> int: ...