Use `split_first_chunk` instead of splitting manually #25412

Job	Run time
Rustfmt	30s
Determine CI jobs to run	12s
Check JS	8s
Clang format	11s
Clippy	5m 1s
Check wasmtime	3m 41s
Monolith Checks	2m 59s
Check wasmtime-cli	3m 23s
no_std checks	51s
Check cranelift-codegen	57s
Check wasmtime-bench-api	1m 15s
Check wasmtime-c-api	1m 19s
Cargo deny	0s
Cargo vet	0s
Check Windows ARM64	0s
Doc build	0s
Test C-API ${{ matrix.os }}	0s
Tests on i686-unknown-linux-gnu	54s
Tests on armv7-unknown-linux-gnueabihf	1m 15s
Nightly tests	0s
Test DWARF debugging	0s
Test wasmtime-fuzzing	0s
Test wasi-nn (${{ matrix.feature }}, ${{ matrix.os }})	0s
Build wasi-preview1-component-adapter	0s
Build wasmtime-target-wasm32	0s
Test the min-platform example	0s
Run benchmarks	0s
Release build for ${{ matrix.build }}	0s
Meta deterministic check	0s
Miri	0s
verify-publish	0s
Cargo vet failed on a Pull Request	0s
Build wasi-preview1-component-adapter-provider	0s
Record the result of testing and building steps	1s
push-tag	0s
	22m 37s

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