perf: avoid allocating in binary and/or when possible

[anderseknert]

Avoid allocation in & and | calls when either of the operands is an empty set.

[github-actions]

Benchmark Regression Detected

Commit d4252139230e1a2a355b10267e86a58fc7e1fb0b introduced benchmark regressions (threshold: >25% ns/op increase).

Package	Benchmark	Regression
v1/ast	BenchmarkFromBuiltinNames/two_parts-4	+166%
v1/ast	BenchmarkNoASTTypeAllocatesOnAppendToBufferOfStringLength/not,_explicit_body,_multi-line-4	+26%
v1/ast	BenchmarkFromBuiltinNames/no_match-4	+25%

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