perf(runtime): add typed-slice fast paths to in operator

[mingrammer]

Summary

runtime.In (called by the OpIn opcode for the in operator) uses reflect to iterate its right-hand side. The reflect path is correct for any slice type, but it pays one heap allocation per element on every typed slice, because reflect.Value.Index(i).Interface() must box the element when the slice's element type is not already interface{}.

For []any the boxing is a no-op (the cell is already an interface), so the existing path is already zero-alloc-per-element. For []string, []float64, []int64, []int, and []bool it adds N heap allocations per in evaluation, which is a significant tax when in runs in a hot loop (e.g. rule engines or expression-based filters over candidate lists).

This PR adds a small type-switch at the top of In for those five common shapes. Each case uses a pure-Go for ... range loop, so no reflect, no per-element boxing, no Equal() round-trip.

Behavior preserved

On a needle/element type mismatch the case falls through to the existing reflect path, so Equal()'s cross-type promotion semantics are preserved. For example, an int needle against []float64 still matches via numeric promotion. The existing test suite is untouched and still passes; new tests in vm/runtime/runtime_test.go cover hit/miss for each fast path, an empty typed slice, cross-type needles, and unchanged []any semantics.

Benchmarks

Apple M4 Pro, darwin/arm64, go test -benchtime=1s ./vm/runtime/:

Bench	before	after	speedup
StringSlice/N=8	112.8 ns, 6 allocs	18.96 ns, 1 alloc	6.0×
StringSlice/N=64	659.8 ns, 34 allocs	31.69 ns, 1 alloc	20.8×
StringSlice/N=256	2240 ns, 130 allocs	60.28 ns, 1 alloc	37.2×
Float64Slice/N=8	85.1 ns, 6 allocs	14.99 ns, 1 alloc	5.7×
Float64Slice/N=64	442.1 ns, 34 allocs	23.66 ns, 1 alloc	18.7×
Float64Slice/N=256	1794 ns, 130 allocs	169.1 ns, 1 alloc	10.6×
Int64Slice/N=8	82.0 ns, 6 allocs	14.77 ns, 1 alloc	5.6×
Int64Slice/N=64	973.8 ns, 34 allocs	23.15 ns, 1 alloc	42.1×
Int64Slice/N=256	1610 ns, 130 allocs	166.0 ns, 1 alloc	9.7×
AnySliceOfString/N=*	unchanged	unchanged	—

The remaining 1 alloc/op is the call-site itself boxing the needle into any when calling runtime.In; it lives outside the changed code.

Test plan

• go test ./vm/runtime/... (new + existing)
• go test ./... (full suite, all green)
• go vet ./...
• go test -bench=BenchmarkIn -benchmem ./vm/runtime/ (numbers above)