Switch windows build to fully dynamic

Refactor where we store build outputs, and support a fully dynamic loading
model on windows so the base executable has no special dependencies thus
doesn't require a special PATH.

llm/shim_ext_server_windows.go

@@ -0,0 +1,29 @@
+package llm
+
+import (
+	"embed"
+	"log"
+	"os"
+	"strings"
+)
+
+//go:embed llama.cpp/gguf/build/windows/*/lib/*.dll
+var libEmbed embed.FS
+
+func updatePath(dir string) {
+	pathComponents := strings.Split(os.Getenv("PATH"), ";")
+	for _, comp := range pathComponents {
+		// Case incensitive
+		if strings.ToLower(comp) == strings.ToLower(dir) {
+			return
+		}
+	}
+	newPath := strings.Join(append(pathComponents, dir), ";")
+	log.Printf("Updating PATH to %s", newPath)
+	os.Setenv("PATH", newPath)
+}
+
+func verifyDriverAccess() error {
+	// TODO if applicable
+	return nil
+}