Refactor algo selection logic and introduce symmetric_memory env (#741)

This PR refactors the algorithm selection logic in MSCCL++ and
introduces support for symmetric memory configuration through
environment variables.


1. Algorithm Selection Refactoring
Use separate class for algo selection. Could introduce more complex
logic for algo selection based on message size, arch, if cuda graph is
enabled and memory allocation method

2. Symmetric Memory Support
Introduced symmetricMemory parameter in algorithm context key
generation. Remove disableChannelCache env as is ambiguous

3. Add new args for build_default_algorithms 
Add flag_buffer, and flag_buffer_size args to build default algorithm.
Then we could use unified flag buffer for different algorithms, avoid
application hanging when switch algo for different message size.

---------

Co-authored-by: chhwang <8018170+chhwang@users.noreply.github.com>
Co-authored-by: Qinghua Zhou <qinghuazhou@microsoft.com>
Co-authored-by: Caio Rocha <caiorocha@microsoft.com>

python/mscclpp/ext/algorithm_collection_builder.py

@@ -3,7 +3,7 @@
 
 from __future__ import annotations
 from typing import Union
-from mscclpp._core.algorithm import Algorithm, AlgorithmBuilder, AlgorithmCollection
+from mscclpp._core.algorithm import Algorithm, AlgorithmBuilder, AlgorithmCollection, get_default_flag_buffer
 import atexit
 
 from mscclpp._mscclpp import CppAlgorithmCollectionBuilder
@@ -29,6 +29,7 @@ class AlgorithmCollectionBuilder:
         if not hasattr(self, "_initialized"):
             self._builder = CppAlgorithmCollectionBuilder.get_instance()
             self._initialized = True
+            self._flag_buffer = None
 
     def add_algorithm_builder(self, algorithm_builder: Union[AlgorithmBuilder, Algorithm]):
         if isinstance(algorithm_builder, AlgorithmBuilder):
@@ -50,8 +51,17 @@ class AlgorithmCollectionBuilder:
         collection = self._builder.build()
         return AlgorithmCollection(collection)
 
-    def build_default_algorithms(self, scratch_buffer: int, scratch_buffer_size: int, rank: int) -> AlgorithmCollection:
-        native_collection = self._builder.build_default_algorithms(int(scratch_buffer), scratch_buffer_size, rank)
+    def build_default_algorithms(
+        self,
+        scratch_buffer: int,
+        scratch_buffer_size: int,
+        rank: int,
+    ) -> AlgorithmCollection:
+        if self._flag_buffer is None:
+            self._flag_buffer = get_default_flag_buffer()
+        native_collection = self._builder.build_default_algorithms(
+            int(scratch_buffer), scratch_buffer_size, self._flag_buffer.data.ptr, self._flag_buffer.nbytes, rank
+        )
         return AlgorithmCollection(native_collection)