perf(engine): paragraph operator dedup + table cell sanitize-once (F5+F6)

[DemchaAV]

Two render-path efficiency optimizations. F6 is byte-identical; F5 is visually identical (emits fewer content-stream operators, same rendering) — guarded by the visual-regression suite plus a content-stream operator-count test.

F5 — paragraph render writes font/colour operators only on change

The paragraph render handler emitted a setFont (Tf) and setNonStrokingColor (rg) operator for every text span, even across the spans of a single-style paragraph (a long body wraps into many spans → as many redundant operator pairs). It now tracks the last-written (font, size) and colour across the paragraph's q…Q block and re-emits only on a real change, invalidating after inline images/shapes (which run their own graphics-state ops).

• Rendered output is unchanged — the skipped operators were redundant no-ops. Guarded by the visual-regression suite plus ParagraphTextStateDedupTest, which renders a one-page single-style paragraph and asserts exactly one Tf across multiple drawn spans (Tj/TJ).

F6 — table cell text sanitized once per cell instead of three times

Resolving a table ran each cell's lines through sanitizeCellLines separately in the natural-width, natural-height and resolve passes — rebuilding the list and its per-line control-character cleanup up to three times per cell. The sanitized lines are now computed once when the logical grid is built (LogicalCell.sanitizedLines) and reused by all three passes.

• Byte-identical (sanitization is deterministic) — covered by the existing table snapshot/visual tests. Removes the dominant per-cell layout allocation on large tables.

Verification

• ./mvnw verify -pl . — BUILD SUCCESS, 1146 tests, 0 failures (checkstyle + SpotBugs + javadoc).

Deferred (follow-up)

• F6 render side: carry the resolved per-line cell width forward so PdfTableRowFragmentRenderHandler stops re-measuring at render — needs a TableResolvedCell model change, tracked separately (the render-side sanitizeLines also trims, so it is not a pure duplicate of the layout sanitize).