limit the number of VM regs to 16 (RV32e) #794

Job	Run time
Build binaries	3m 33s
Examples	7m 40s
CLI	4m 21s
Test (ubuntu-latest)	2m 24s
Test (runs-on, runner=8cpu-linux-arm64, run-id=12654917385)	1m 40s
Test (macos-latest)	2m 13s
Formatting & Clippy	28s
Test (Go) (ubuntu-latest)	1m 22s
Test (Go) (runs-on, runner=8cpu-linux-arm64, run-id=12654917385)	1m 4s
Test (Go) (macos-latest)	1m 45s
Test (Go) (windows-latest)	3m 32s
	30m 2s

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