WASM PVM: Check for floats in the Fast Exec runtime

There has been a long standing issue in the rollup node, where it would happily
use WASMER to execute a kernel featuring floats. Under the hood, the culprit is
actually the Fast Exec runtime, which is not defensive enough when loading a
new kernel.

This patch should fix this shortcoming, and ensure no commitment are wrongfully
posted when a rollup ends up with a kernel featuring floats.

Manually testing the MR

Best proof that it work is a red CI as long as !14145 (merged) is not merged.

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