Fix TORCHAO_SKIP_LOADING_SO_FILES behavior (#3189)

**Summary:** Today, if users want to force skip loading the .so
files, they can pass in `TORCHAO_SKIP_LOADING_SO_FILES=1`.
However, if they pass in `TORCHAO_SKIP_LOADING_SO_FILES=0` or
`TORCHAO_SKIP_LOADING_SO_FILES=false`, we will still skip loading
these files. This commit fixes this behavior by:

1. Renaming this env var to `TORCHAO_FORCE_SKIP_LOADING_SO_FILES`
2. Only accepting value of "1" for this env var

**Test Plan:**

```
$ TORCHAO_FORCE_SKIP_LOADING_SO_FILES=1 python -c "import torchao"
Skipping import of cpp extensions due to TORCHAO_FORCE_SKIP_LOADING_SO_FILES=1

\# No effect
$ TORCHAO_FORCE_SKIP_LOADING_SO_FILES=0 python -c "import torchao"
$ TORCHAO_FORCE_SKIP_LOADING_SO_FILES=False python -c "import torchao"
$ TORCHAO_FORCE_SKIP_LOADING_SO_FILES=false python -c "import torchao"
```

Author: andrewor14

torchao/__init__.py

@@ -45,9 +45,12 @@ def _parse_version(version_string):
 
 
 skip_loading_so_files = False
-if bool(os.getenv("TORCHAO_SKIP_LOADING_SO_FILES", False)):
+force_skip_loading_so_files = (
+    os.getenv("TORCHAO_FORCE_SKIP_LOADING_SO_FILES", "0") == "1"
+)
+if force_skip_loading_so_files:
     # user override
-    # users can set env var TORCH_INCOMPATIBLE=1 to skip loading .so files
+    # users can set env var TORCHAO_FORCE_SKIP_LOADING_SO_FILES=1 to skip loading .so files
     # this way, if they are using an incompatbile torch version, they can still use the API by setting the env var
     skip_loading_so_files = True
 # if torchao version has "+git", assume it's locally built and we don't know
@@ -80,10 +83,15 @@ def _parse_version(version_string):
 
 
 if skip_loading_so_files:
-    logger.warning(
-        f"Skipping import of cpp extensions due to incompatible torch version {torch.__version__} for torchao version {__version__} \
-        Please see GitHub issue #2919 for more info"
-    )
+    if force_skip_loading_so_files:
+        logger.warning(
+            "Skipping import of cpp extensions due to TORCHAO_FORCE_SKIP_LOADING_SO_FILES=1"
+        )
+    else:
+        logger.warning(
+            f"Skipping import of cpp extensions due to incompatible torch version {torch.__version__} for torchao version {__version__} \
+            Please see https://github.com/pytorch/ao/issues/2919 for more info"
+        )
 else:
     try:
         from pathlib import Path