feat(installer): *always* force-reinstall

This has repeatedly shown itself useful in fixing install issues,
especially regarding pytorch CPU/GPU version, so there is little
downside to making this the default.

Performance impact of this should be negligible. Packages will
be reinstalled from pip cache if possible, and downloaded only if
necessary. Impact may be felt on slower disks.

installer/lib/installer.py

@@ -220,10 +220,11 @@ class InvokeAiInstance:
 
         pip = local[self.pip]
 
-        (
+        _ = (
             pip[
                 "install",
                 "--require-virtualenv",
+                "--force-reinstall",
                 "--use-pep517",
                 str(src) + (optional_modules if optional_modules else ""),
                 "--find-links" if find_links is not None else None,