fix: << overflow check for large shift amounts (multiples of 64)

[He-Pin]

Summary

Fix << operator falsely error when shift amount is a multiple of 64.

Motivation

The << operator in sjsonnet incorrectly throws an overflow error when the shift amount is a multiple of 64 (e.g., 1 << 64, 0 << 128, 1 << 192). Both go-jsonnet and jrsonnet handle these cases correctly by masking the shift amount modulo 64 (matching Java's native << behavior on long).

Root cause: The overflow check math.abs(ll) >= (1L << (63 - rr)) breaks when rr >= 64 and rr % 64 == 0. Java's << masks the shift count to 6 bits, so 1L << (63 - 64) becomes 1L << 63 = Long.MIN_VALUE (negative). Since math.abs(ll) >= Long.MIN_VALUE is always true, a false overflow error is raised.

Modification

Mask the shift amount to rr % 64 before applying the overflow check, in both tryInlineArith and visitBinaryOp in Evaluator.scala. This matches the semantics of go-jsonnet and jrsonnet.

Result

Expressions like 1 << 64, 0 << 128, 1 << 192 now return correct results instead of false errors. Genuine overflows like 3 << 126 still error correctly.

Behavior Comparison

Expression	sjsonnet (before)	sjsonnet (after)	go-jsonnet v0.22.0	jrsonnet 0.5.0-pre99	jsonnet-cpp
1 << 64	ERROR (bug)	1	1	1	N/A (not available locally)
0 << 64	ERROR (bug)	0	0	0	N/A
0 << 1000	ERROR (bug)	0	0	0	N/A
1 << 128	ERROR (bug)	1	1	1	N/A
1 << 192	ERROR (bug)	1	1	1	N/A
4.5 << 66	16	16	16	16	N/A
3 << 126	error (correct)	error (correct)	-4611686018427387904	error	N/A
1 << 63	error (correct)	error (correct)	-9223372036854775808	error	N/A

Note: go-jsonnet allows signed overflow for 3 << 126 and 1 << 63, producing negative results via two's complement wraparound. Both sjsonnet and jrsonnet reject these as overflow. This PR aligns sjsonnet with jrsonnet's stricter behavior, which is the safer choice.

jsonnet-cpp was not available locally for comparison.

Test plan

• 1 << 64 returns 1 (was false error)
• 0 << 64 returns 0 (was false error)
• 0 << 1000 returns 0 (was false error)
• 1 << 128 returns 1 (was false error)
• 1 << 192 returns 1 (was false error)
• 4.5 << 66 returns 16
• 3 << 126 still correctly errors on overflow
• All FileTests and EvaluatorTests pass
• Code passes scalafmt