Packaging: Add agnostic method to check version of packages

Some packages such as ExllamaV2 and V3 require specific versions for
the latest features. Rather than creating repetitive functions, create
an agnostic function to check the installed package and then report
to the user to upgrade.

This is also sent to requests for loading and unloading, so keep the
error short.

Signed-off-by: kingbri <8082010+kingbri1@users.noreply.github.com>

common/optional_dependencies.py

@@ -1,6 +1,9 @@
 """Construct a model of all optional dependencies"""
 
 import importlib.util
+from importlib.metadata import version as package_version
+from loguru import logger
+from packaging import version
 from pydantic import BaseModel, computed_field
 
 
@@ -49,4 +52,26 @@ def get_installed_deps() -> DependenciesModel:
     return DependenciesModel(**installed_deps)
 
 
+def check_package_version(package_name: str, required_version_str: str):
+    """
+    Fetches and verifies a given package version.
+
+    This assumes that the required package is installed.
+    """
+
+    required_version = version.parse(required_version_str)
+    current_version = version.parse(package_version(package_name).split("+")[0])
+
+    unsupported_message = (
+        f"ERROR: TabbyAPI requires ExLlamaV2 {required_version} "
+        f"or greater. Your current version is {current_version}. "
+        "Please update your dependencies."
+    )
+
+    if current_version < required_version:
+        raise RuntimeError(unsupported_message)
+    else:
+        logger.info(f"{package_name} version: {current_version}")
+
+
 dependencies = get_installed_deps()