modules/zstd: Add buffer library

This commit adds a DSLX Buffer library that provides the Buffer struct,
and helper functions that can be used to operate on it. The Buffer
is meant to be a storage for data coming from the channel. It acts like
a FIFO, allowing data of any length to be put in or popped out of it.
Provided DSLX tests verify the correct behaviour of the library.

Internal-tag: [#50221]
Signed-off-by: Robert Winkler <[email protected]>

Author: rw1nkler

xls/modules/zstd/BUILD

@@ -0,0 +1,39 @@
+# Copyright 2023 The XLS Authors
+#
+# 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.
+
+# Build rules for XLS ZSTD codec implementation.
+
+load(
+    "//xls/build_rules:xls_build_defs.bzl",
+    "xls_dslx_library",
+    "xls_dslx_test",
+)
+
+package(
+    default_applicable_licenses = ["//:license"],
+    default_visibility = ["//xls:xls_users"],
+    licenses = ["notice"],
+)
+
+xls_dslx_library(
+    name = "buffer_dslx",
+    srcs = [
+        "buffer.x",
+    ],
+)
+
+xls_dslx_test(
+    name = "buffer_dslx_test",
+    library = ":buffer_dslx",
+)