fix: use ValueError instead of assert on argument checks

[chenpan321]

This pull request fixes a small issue on script python/merge_lora_into_ggml.py.

Program should always fail if arch_version or data format does not satisfy the preconditions in the program. However, the file merge_lora_into_ggml.py uses assert statements, sometimes being ignored under high optimization level. We uses if-statements here, where those preconditions would always execute, whether the environment enable assert stateuements or not.

Ref: https://stackoverflow.com/questions/61826628/what-is-the-advantage-if-any-of-using-assert-over-an-if-else-condition . Here, our checks are still in effect when -O flag is enabled, so if __debug__: (implied in assert statements) is not necessary.

[saharNooby]

That was a revelation for me! I did not know that Python is allowed to disable assertions.

This means we need to rewrite all Python code in rwkv.cpp to get rid of assertions and replace them with ifs. Probably later.