Unroll constantly to improve performance of multi-arity calls

Description

This was found to be a hot spot when testing some Specter use cases.

Review of common uses of constantly shows that the arity 1 case is the most common use of `constantly` in the wild, so only unrolled to two arguments.

Perf test:

Patch: 0001-CLJ-2228-Improve-performance-of-constantly.patch

Prescreened by: Alex Miller

Environment

None

Assignee

Unassigned

Reporter

import

Labels

Approval

Prescreened

Patch

Code and Test

Priority

Minor
Configure