perf: speed-up cycle-retry logic

[MichaReiser]

• Avoid an atomic load in the most common case where the query isn't participating in a
  cycle.
• Only perform the test in fetch_cold (with_retry) because memos returned by fetch_hot are always finalized.

[netlify]

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[codspeed-hq]

CodSpeed Performance Report

Merging #861 will improve performances by 5.88%

_{Comparing MichaReiser:first-test-cycle-heads (42f6356) with master (7edce6e)}

Summary

⚡ 2 improvements
✅ 10 untouched benchmarks

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	amortized[InternedInput]	3.2 µs	3 µs	+5.88%
⚡	new[InternedInput]	5.4 µs	5.1 µs	+5.18%