feat: validate and repair malformed page boxes

Validate and repair the page-boundary boxes (MediaBox, CropBox, TrimBox,
ArtBox, BleedBox) of input PDFs in triage(), following PDF 2.0:

- Coerce coordinates written in invalid exponential notation, stored by
  qpdf/pikepdf as strings (#1398).
- Normalize rectangles whose corners are given in reversed order, which
  previously crashed with NegativeDimensionError (#1526).
- Clamp a crop/trim/art/bleed box that extends outside the MediaBox to
  their intersection, or discard it when the intersection is empty, which
  previously produced a zero-height effective page some viewers rejected
  (#1400).

When a box is discarded, clamped, or reinterpreted, a warning recommends
visual inspection of the output. pdfinfo box reading shares the same
coercion helper so PdfInfo no longer crashes on malformed boxes.

Supersedes PR #1691. Thanks @ajdlinux.

Closes #1398, #1526, #1400

docs/releasenotes/version17.md

@@ -5,6 +5,18 @@
 
 ## v17.6.0
 
+- OCRmyPDF now validates and repairs malformed page-boundary boxes
+  (``/MediaBox``, ``/CropBox``, ``/TrimBox``, ``/ArtBox``, ``/BleedBox``) in its
+  input, following the PDF 2.0 specification. Coordinates written in invalid
+  exponential notation are reinterpreted ({issue}`1398`); rectangles whose
+  corners are given in reversed order are normalized, which previously crashed
+  with ``NegativeDimensionError`` ({issue}`1526`); and a crop/trim/art/bleed box
+  that falls outside the MediaBox is clamped to their intersection, or discarded
+  when that intersection is empty, which previously produced an output with a
+  zero-height effective page that some viewers refused to open ({issue}`1400`).
+  When a box is discarded, clamped, or reinterpreted, OCRmyPDF logs a warning
+  recommending visual inspection of the output. Thanks @ajdlinux for the initial
+  fix in PR #1691.
 - OCRmyPDF now discards an embedded Adobe full-text search index
   (``/Root/PieceInfo/SearchIndex``) from its output. This proprietary index,
   produced by Acrobat's "Embed Index" feature, is read only by Adobe Acrobat;