Fix fuel accounting in tests on MacOS

[jeffcharles]

Description of the change

There shouldn't be any functional changes. This just adjusts how we initialize modules in tests so we consistently use a file-backed initialization image that skips copying active data segments into linear memory.

Why am I making this change?

The tests stopped passing on MacOS due to fuel consumed becoming much higher after we updated to Wasmtime 46. Wasmtime 46, in this change, started executing startup code in Wasm instead of in the host environment. On Linux, this doesn't really make a difference to fuel accounting in practice. On MacOS however, the startup function performs operations to copy memory. I've put a comment in the code change explaining the details.

Checklist

• I've updated the default plugin import namespace and incremented the major version of javy-plugin-api if the QuickJS bytecode has changed.
• I've updated the relevant CHANGELOG files if necessary. Changes to javy-cli, javy-plugin, and javy-plugin-processing do not require updating CHANGELOG files.
• I've updated the relevant crate versions if necessary. Versioning policy for library crates
• I've updated documentation including crate documentation if necessary.