Draft: RISC-V/PROTO: Fully implement riscv protocol environment module

Closes RV-374

What

Removes all stubs from Riscv module in lib_protocol_envioronment.

Why

Have a full implementation with no gaps for the RISC-V pvm inside the protocol.

How

Replace the stubs with calls to the relevant functions in octez-riscv-pvm

Manually testing the MR

make -C src/riscv build
make octez-layer1
dune exec tezt/tests/main.exe -- riscv

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR