Bug(expr): split/rsplit with maxsplit=-1 discard the input entirely

[uberware]

Summary

split('a,b,c', ',', -1) returns [] — the input is discarded. RFC 0006 documents
maxsplit as splitting "at most maxsplit times" and defines nothing for a negative value,
so no reading supports returning an empty list. Python (whose str.split the function
otherwise follows) treats a negative maxsplit as "unlimited", returning ["a", "b", "c"].

Versions

• openjd-model 0.11.1 and 0.11.2 from PyPI
• openjd-rs main at 1a89f3a — still reproduces

Reproduction

from openjd.expr import parse_expression
for src in ("split('a,b,c', ',', -1)", "rsplit('a,b,c', ',', -1)"):
    r = parse_expression(src).evaluate_with_metrics()
    print(src, "->", str(r.value))    # -> [] for both

Expected vs actual

Expression	Expected	Actual
split('a,b,c', ',', -1)	["a", "b", "c"] (Python's reading) or an error	[]
rsplit('a,b,c', ',', -1)	["a", "b", "c"] or an error	[]

Either the Python reading or an explicit rejection would be defensible; silently returning
[] loses data with no textual support in the spec.