refactor(isthmus): improve extensibility of SubstraitRelVisitor #1600

Job	Run time
Security validation	8s
Build and Test Java	4m 36s
Check editorconfig	7s
osv-scanner (isthmus)	1m 49s
osv-scanner (core)	1m 47s
Lint commits for semantic-release	12s
osv-scanner (isthmus-cli)	1m 30s
Build Examples	3m 54s
Dry-run release	23s
Build Isthmus Native Image (macOS-latest)	16m 15s
Build Isthmus Native Image (ubuntu-latest)	8m 27s
	39m 8s

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