fix: crash when passing NimNode to static parameter

[zerbina]

Summary

• fix a compiler crash when passing a NimNode to a static parameter
• fix a compiler crash when evaluating a NimNode-returning constant expression

Details

There were two problems:

• nkNimNodeLit wasn't handled in constant data expression by mirgen
• NimNode values returned directly from a VM invocation weren't wrapped in nkNimNodeLit trees

For handling NimNode values in vm.regToNode, the existing deserialization logic for NimNode values in vmcompilerserdes is moved to a separate procedure, so that it can be used by regToNode.

The opcRepr implementation relied on regToNode always returning an unwrapped PNode -- it is adjusted to manually handle NimNode values.

A test covering both issues is added.

Fixes https://github.com/nim-works/nimskull/issues/1448.

[saem]

/merge

[github-actions[bot]]

Merge requested by: @saem

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