fix(wasm): lift hostcall fuel limit for large component outputs

[oglassdev]

Fixes #97.

Wasmtime's default hostcall fuel (128 MiB) charges a whole Val (32 bytes) for each lifted list element. That capped a component call's list<u8> output at about 4 MiB. Window builds hit the cap somewhere between 10x and 12x the jsx golden case and failed with fuel allocated for hostcalls has been exhausted.

new_store now sets hostcall fuel to memory_bytes × size_of::<Val>(). That's the cost of lifting the largest list<u8> that fits in guest memory, so any real output can be returned. Lists that alias the same guest buffer still hit a finite cap, which wouldn't hold with usize::MAX.

• Fuel resets for each lift, so reused stores don't run out over time. Host→guest arguments aren't charged.
• new_store is the only place stores are created.
• The new test lifts_byte_list_beyond_default_hostcall_fuel lifts 5 MiB through a new bytes export on the fixture. It fails without the fix.

Window bench/authoring cold builds, which failed at 12x/15x before this change:

Scale	jsx wall / build (ms)	fn wall / build (ms)
12x	310 / 241	302 / 234
15x	366 / 286	359 / 289
30x	620 / 517	597 / 504

Each lifted byte still costs about 32 bytes of host memory. A typed byte-list fast path is listed in chunkzero/window#58.

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