Reset the proof version and digest label at the first production release #364

From this review comment on #363.

Every protocol change bumps two counters:

• Proof::VERSION in crates/leanvm/src/lib.rs, the u16 after the LVMP magic in a proof's bytes;
• the program digest's domain label, leanvm-rv64im-N, in crates/leanvm_core/src/cpu/mod.rs and python-verifier/verifier.py.

Wave D bumps them once per PR, so by the first production release they will count development iterations no deployed proof ever used.

To do at the first production release

• Reset Proof::VERSION to 1.
• Reset the digest label to a release name, for example leanvm-rv64im-v1, in Rust and Python together.
• From then on, bump each only for a change to what a released proof says.

Both resets change the proof bytes, so they go in the release PR itself, with the fixtures and the Python verifier moving together.