[Prototype] Dynamic vadcop

[georgwiese]

Builds on #1542
Fixes #1496

To test:

cargo run -r pil test_data/std/binary_test_dynamic.asm -o output -f --prove-with estark-starky-composite

Steps:

• 8906795:
  • The linker keeps degrees of None
  • When the degree is None, the constant evaluate computes all degrees from $2^5$ to $2^{10}$ (these are constants that can be changed)
  • CompositeBackend implements variable-length by:
    • Instantiating a Backend for each machine and possible size
    • Storing a verification key for each machine and possible size
    • When creating a proof, it picks the backend of the right size and stores the choice in the proof
    • When validating a proof, it selects the verification key given the proof size
  • Automatic witness generation always "choses" the largest available size
• Following commits: Adjust witgen:
  • Each machine already knows its size (prior to this PR), so the current size is explicitly passed whenever a fixed column value is read.
  • The size of each machine is still initialized to the maximum.
  • In BlockMachine::take_witness_col_values, we down-size the machine as needed

Current blockers:

• It seems like columns need to have a size when the PIL is analyzed. We unwrap here because RepeatedArray needs to know the size.
  • So any dynamic machine with an array like col fixed foo = [1, 2, 3]* fails
  • This is causing some test failures and blocks making the main VM dynamic