feat(runtime,serverless): add V8 heap snapshots

[QuiiBz]

Add a build.rs in crates/serverless to generate a snapshot.bin file containing a V8 heap snapshot of the js-runtime code, which is then used when booting isolates (which only contains the user's code). It's not mandatory to use a snapshot to start a Lagon runtime, but it currently reduces the cold start by a lot. Here's a before/after running 6 times a cold start:

Before (or by not providing a V8 snapshot):

Statistics: IsolateStatistics { cpu_time: 5.660791ms, memory_usage: 583232 }
Statistics: IsolateStatistics { cpu_time: 3.700791ms, memory_usage: 583232 }
Statistics: IsolateStatistics { cpu_time: 3.214416ms, memory_usage: 583232 }
Statistics: IsolateStatistics { cpu_time: 2.923625ms, memory_usage: 583232 }
Statistics: IsolateStatistics { cpu_time: 3.115166ms, memory_usage: 583232 }
Statistics: IsolateStatistics { cpu_time: 3.400375ms, memory_usage: 583232 }

After, providing a V8 snapshot:

Statistics: IsolateStatistics { cpu_time: 3.1ms, memory_usage: 621864 }
Statistics: IsolateStatistics { cpu_time: 902.291µs, memory_usage: 621864 }
Statistics: IsolateStatistics { cpu_time: 651.5µs, memory_usage: 621864 }
Statistics: IsolateStatistics { cpu_time: 853.208µs, memory_usage: 621864 }
Statistics: IsolateStatistics { cpu_time: 584.375µs, memory_usage: 621864 }
Statistics: IsolateStatistics { cpu_time: 842.125µs, memory_usage: 621864 }

The first cold start goes from ~5ms to ~3ms, and subsequent cold starts goes from ~3ms to ~800us.

About

Following #255:

• Run the tests with and without the heap snapshot, using the ignore-snapshot feature
• Split sync and async bindings to globalThis.LagonSync and globalThis.LagonAsync, because async bindings can't be serialized - only sync bindings are

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