Avoid redundant result iterator restarts

[ilkecan]

Summary

Avoid redundant paragraph and text-line restarts when a ResultIterator is already at the required physical start position.

The reading-order setup repeatedly copied iterators and restarted them even when PageIterator::Next() had just placed them at a paragraph or text-line start. On sparse layouts with many blocks, those no-op restarts become costly repeated scans.

Change

• guards paragraph and row restarts with the physical PageIterator::IsAtBeginningOf() predicate
• uses the same physical predicate to detect paragraph transitions after PageIterator::Next()
• adds focused LTR and RTL coverage for block, paragraph, and text-line iteration, including logical versus physical starts and an interior word

Performance

GCC 15.2 RelWithDebInfo build, with OEM 3, PSM 11 and OMP_THREAD_LIMIT=1:

Input	Before	After
input-4267x3200.png	52.90 s	8.41 s
#4430 page.png	>300 s	95.62 s

The minimal reproducer's OCR output is identical to the baseline from main.
The reproducer, input-4267x3200.png, is generated by repeating a 16x16 texture-only image across a 4267x3200 canvas.

input-4267x3200.png

background-tile-16.png

Related to #4430.

Validation

• Full CTest suite: 62/62 passed.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 7 complexity · 0 duplication

Metric	Results
Complexity	7
Duplication	0

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[Copilot]

Pull request overview

Optimizes ResultIterator navigation by avoiding redundant scans when already at a physical paragraph or text-line start.

Changes:

• Guards paragraph and row restarts with physical-position checks.
• Uses physical starts to detect paragraph transitions.
• Adds LTR and RTL iterator coverage.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/ccmain/resultiterator.cpp	Avoids unnecessary iterator restarts and paragraph scans.
unittest/resultiterator_test.cc	Tests logical and physical starts across iteration levels.

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