[rhi] MetalCommandList store unique_ptr to resource set (#8312)

Issue: #

### Brief Summary

Directly storing a pointer to the resource set is bad because the
resource set can be destroyed before the command list is done.

### Walkthrough

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copilot:walkthrough
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### <samp>🤖 Generated by Copilot at f7a1b72</samp>

* Initialize members to avoid dangling pointers and use
`std::unique_ptr` to manage shader resource set lifetime in
`MetalCommandList` class
([link](https://github.com/taichi-dev/taichi/pull/8312/files?diff=unified&w=0#diff-5b304e188996abd217fad85fd8b2434e729ad9c089eb9ef48a848c0fcc74d614L268-R269),
)
* Copy shader resource set argument instead of modifying it and cast it
to `MetalShaderResourceSet` pointer in `bindShaderResourceSet` method
([link](https://github.com/taichi-dev/taichi/pull/8312/files?diff=unified&w=0#diff-c350a27659df1ebcf2c854e2c21a80f82de87d3b325a80e00f6a6dd6ca53303bL428-R429))

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

taichi/rhi/metal/metal_device.h

@@ -265,8 +265,8 @@ class MetalCommandList final : public CommandList {
   MTLCommandBuffer_id cmdbuf_;
 
   // Non-null after `bind*` methods.
-  const MetalPipeline *current_pipeline_;
-  const MetalShaderResourceSet *current_shader_resource_set_;
+  const MetalPipeline *current_pipeline_{nullptr};
+  std::unique_ptr<MetalShaderResourceSet> current_shader_resource_set_{nullptr};
 };
 
 class MetalStream final : public Stream {

taichi/rhi/metal/metal_device.mm

@@ -425,7 +425,9 @@ MTLTextureUsage usage2mtl(ImageAllocUsage usage) {
                                                   int set_index) noexcept {
   RHI_ASSERT(res != nullptr);
   RHI_ASSERT(set_index == 0);
-  current_shader_resource_set_ = (MetalShaderResourceSet *)res;
+  MetalShaderResourceSet *res_metal = (MetalShaderResourceSet *)res;
+  current_shader_resource_set_ =
+      std::make_unique<MetalShaderResourceSet>(*res_metal);
   return RhiResult::success;
 }