WASM/PVM: Integrates EOL / SOL inputs and read a whole inbox at once

Context

Fixes #3157 (closed)

This MR implements the PVM scheduling: reads all inputs from the inbox at a given level and put them in the input buffer, followed by at most p kernel_next, p being 10_000 for now but only as a placeholder.

Also handles the representation of SOL/EOL introduced in !6549 (merged) in the PVM (see commit description for the rationale)

TODO:

• Fix the existing tests
• Test the scheduling

Manually testing the MR

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).
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