chore: simplify parser & reduce allocations #515

Job	Run time
Build wasm	2m 14s
Run tests on macOS arm64 (Apple M1)	1m 8s
Run tests on Linux arm64	4m 22s
Run tests on Linux x86 (nightly, no default features)	1m 16s
Run tests on Linux armv7	4m 27s
Run tests on Linux x86 (stable, no default features)	58s
Run tests on Linux x86 (nightly)	1m 26s
Run tests on Linux x86 (stable)	55s
	16m 46s

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