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)

[github-actions]

Automated Reviewer Suggestions

Based on the git blame history of the changed files, we recommend the following reviewers:

• Contributors with relevant context: @Yicong-Huang
  You can notify them by mentioning @Yicong-Huang in a comment.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 52.88%. Comparing base (80de40f) to head (265b25f).
⚠️ Report is 2 commits behind head on release/v1.2.

Additional details and impacted files

@@               Coverage Diff               @@
##             release/v1.2    #7529   +/-   ##
===============================================
  Coverage           52.88%   52.88%           
+ Complexity           2527     2526    -1     
===============================================
  Files                1078     1078           
  Lines               42367    42367           
  Branches             4565     4565           
===============================================
  Hits                22405    22405           
  Misses              18645    18645           
  Partials             1317     1317           

Flag	Coverage Δ		*Carryforward flag
access-control-service	64.35% <ø> (ø)
agent-service	34.36% <ø> (ø)		Carriedforward from 9ead9e9
amber	53.00% <100.00%> (ø)
computing-unit-managing-service	1.65% <ø> (ø)
config-service	56.06% <ø> (ø)
file-service	61.72% <ø> (ø)
frontend	47.29% <ø> (ø)		Carriedforward from 9ead9e9
pyamber	93.07% <ø> (ø)		Carriedforward from 9ead9e9
python	90.88% <ø> (ø)		Carriedforward from 9ead9e9
workflow-compiling-service	58.69% <ø> (ø)

*This pull request uses carry forward flags. Click here to find out more.

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