fix(workflow-operator, v1.2): Text Input operator using offset with an empty limit emits no rows

[eugenegujing]

What changes were proposed in this PR?

Backport of #7347 to release/v1.2, cherry-picked from main commit 91235fb (clean, no conflicts).

TextInputSourceOpExec computed its line window as slice(offset, offset + limit.getOrElse(Int.MaxValue)). With an Offset set and the Limit left empty, the addition overflows Int to a negative bound, which Scala 2.13's Iterator.slice clamps to 0 and then returns an empty iterator — so the operator silently emitted zero rows while the workflow reported success. Any Offset ≥ 1 with an empty Limit is affected, and an explicit large Limit (e.g. Int.MaxValue) overflows the same way. This contradicts the Limit property's own description, "Leave empty to read all lines."

The fix replaces the slice with drop(offset) + take(limit), the same idiom the CSV, Arrow, and JSONL scan sources already use. There is no addition, so nothing can overflow; every configuration that previously worked is unchanged.

Any related issues, documentation, discussions?

Backport of #7347 (originally closed #7346).

How was this PR tested?

The 7 regression tests from #7347 come along with the cherry-pick. On this branch:

sbt "WorkflowOperator/testOnly org.apache.texera.amber.operator.source.scan.text.TextInputSourceOpDescSpec"
# 15 tests, all passed (8 pre-existing on release/v1.2 + 7 new)
# (main has 17: two getPhysicalOp/propagateSchema coverage tests were added
#  to this spec after v1.2 branched and are unrelated to this fix)

sbt "WorkflowOperator/scalafmtCheck" "WorkflowOperator/Test/scalafmtCheck"
# passed

sbt "WorkflowOperator/scalafixAll --check"
# passed

Was this PR authored or co-authored using generative AI tooling?

Co-authored by: Claude Code (Claude Fable 5)

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