fix(_utils): coerce _is_package_available tuple to bool for flash_attn/vllm checks (#6168)

transformers >= 5.x makes _is_package_available always return a
(exists, version) tuple, which is truthy even when the package is
absent. The flash_attn and vLLM availability checks treated the result
as a bool, so they always entered the "package present" branch:

- flash_attn (CUDA + HIP): the inner import raises when flash-attn is
  not installed, printing a false "Flash Attention 2 installation seems
  to be broken" warning before falling back to xformers.
- is_vLLM_available(): always reported vLLM as installed.

Add a small _package_available() helper that normalises the result to a
bool (handling both the new tuple and the legacy bool return), and route
the three call sites through it.

Fixes #6155

Co-authored-by: Lee Jackson <130007945+Imagineer99@users.noreply.github.com>

unsloth/models/_utils.py

@@ -1264,6 +1264,18 @@ if is_openai_available():
 from transformers import AutoTokenizer
 from transformers.utils.import_utils import _is_package_available
 
+
+def _package_available(pkg_name: str) -> bool:
+    # transformers >= 5.x makes `_is_package_available` always return a
+    # `(exists, version)` tuple, which is truthy even when the package is
+    # absent; older versions returned a plain bool. Normalise to a bool so
+    # callers don't take "package present" branches for missing packages.
+    result = _is_package_available(pkg_name)
+    if isinstance(result, tuple):
+        return bool(result[0])
+    return bool(result)
+
+
 SUPPORTS_BFLOAT16 = False
 HAS_FLASH_ATTENTION = False
 HAS_FLASH_ATTENTION_SOFTCAPPING = False
@@ -1274,7 +1286,7 @@ if DEVICE_TYPE == "cuda":
 
     if major_version >= 8:
         SUPPORTS_BFLOAT16 = True
-        if _is_package_available("flash_attn"):
+        if _package_available("flash_attn"):
             # Check for CUDA linking errors "undefined symbol: _ZNK3c106SymIntltEl"
             try:
                 try:
@@ -1319,7 +1331,7 @@ if DEVICE_TYPE == "cuda":
         HAS_FLASH_ATTENTION = False
 elif DEVICE_TYPE == "hip":
     SUPPORTS_BFLOAT16 = True
-    if _is_package_available("flash_attn"):
+    if _package_available("flash_attn"):
         # Check for CUDA linking errors "undefined symbol: _ZNK3c106SymIntltEl"
         try:
             try:
@@ -1981,7 +1993,7 @@ def is_bfloat16_supported():
 
 
 def is_vLLM_available():
-    return _is_package_available("vllm")
+    return _package_available("vllm")
 
 
 # Patches models to add RoPE Scaling