Update on "[ET-VK] Cache compiled SPIR-V and only recompile when changed"

## Context

As title. Introduce a caching mechanism to store SPIR-V generated in a previous build to avoid re-compiling them.

A shader will not be re-compiled if the source GLSL template is unchanged.

For Meta internal builds, the `etvk.force_shader_rebuild` buck config can be used to force all shaders to be built without using the cache.

Differential Revision: [D71916745](https://our.internmc.facebook.com/intern/diff/D71916745/)

[ghstack-poisoned]

Author: SS-JIA

backends/vulkan/runtime/gen_vulkan_spv.py

@@ -735,7 +735,7 @@ def maybe_replace_u16vecn(self, input_text: str) -> str:
         input_text = input_text.replace("uint16_t", "int")
         return input_text
 
-    def get_md5_checksum(self, file_path: str) -> bool:
+    def get_md5_checksum(self, file_path: str) -> str:
         # Use a reasonably sized buffer for better performance with large files
         BUF_SIZE = 65536  # 64kb chunks