pex: switch to SCIE binary instead of PEX #25004

Job	Run time
Classify changes	5s
Bootstrap Pants, test Rust (macOS13-x86_64)	3m 4s
Bootstrap Pants, test Rust (Linux-ARM64)	1m 40s
Bootstrap Pants, test and lint Rust (Linux-x86_64)	2m 6s
Build wheels (Linux-ARM64)	0s
Ensure PR has release notes	2s
Build wheels (Linux-x86_64)	0s
Build wheels (macOS13-x86_64)	0s
Build wheels (macOS14-ARM64)	0s
Lint Python and Shell	3m 58s
Test Python (Linux-x86_64) Shard 0/10	17m 37s
Test Python (Linux-x86_64) Shard 1/10	17m 32s
Test Python (Linux-x86_64) Shard 2/10	18m 8s
Test Python (Linux-x86_64) Shard 3/10	23m 27s
Test Python (Linux-x86_64) Shard 4/10	35m 29s
Test Python (Linux-x86_64) Shard 5/10	20m 46s
Test Python (Linux-x86_64) Shard 6/10	10m 27s
Test Python (Linux-x86_64) Shard 7/10	16m 35s
Test Python (Linux-x86_64) Shard 8/10	17m 34s
Test Python (Linux-x86_64) Shard 9/10	10m 47s
Test Python (Linux-ARM64)	11m 11s
Test Python (macOS13-x86_64)	24m 30s
Set Merge OK	0s
Merge OK	1s
	3h 54m 59s

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