Fix push constant range validation with multiple entry points

[rjodinchr]

When a program has multiple entry points, and only a subset of them use image/sampler metadata, the SPIR-V shader declares a larger push constant block that accommodates all potential metadata across the program. Previously, the push constant range in the pipeline layout was calculated per entry point in cvk_entry_point::init(). This resulted in a mismatch between the declared SPIR-V push constant block size and the pipeline layout's push constant range size on entry points without metadata usage, triggering Vulkan validation layer errors.

This commit resolves the issue by:

• Moving the complete push constant range calculation from cvk_entry_point to cvk_program::prepare_push_constant_range().
• Consolidating all potential push constant sources (binary constants, push constant kernel arguments, image metadata, and sampler metadata) upfront across the entire program.
• Ensuring the pipeline layout's push constant range consistently covers the maximum declared SPIR-V block size across all entry points.
• Updating the POD buffer size assertion in create_pod_buffer() to precisely match m_entry_point->pod_buffer_size().

[rjodinchr]

Note that we do not see that error in the GitHub CI because the VVL we use is too old.