…e conditions (#3529)

width and height are now treated symmetrically, and updated only if they
are not provided.

---------

Co-authored-by: Stefan <96178532+stefan6419846@users.noreply.github.com>

On first access to any object in a compressed object stream,
parse and cache ALL objects in that stream in one pass.
This avoids O(N²) behavior when many objects from the same
stream are resolved individually during add_page().

PDFs produced by DMS tools like PDFKit.NET DMV10 pack ~2000
objects into a single ObjStm. The previous code scanned the
full header for each lookup, resulting in ~77M function calls
and 5s+ parse times for a 370KB invoice. With batch parsing,
the same file completes in ~0.08s (61x speedup).

Three functions had quadratic behavior that caused hangs on PDFs with
extremely long Name objects (e.g. repeatedly mis-encoded UTF-8 names):

- read_until_regex: searched entire accumulated buffer on each 16-byte
  chunk instead of only the new chunk, and used bytes concatenation
- NameObject.unnumber: rebuilt entire bytes object on each # replacement
- NameObject.renumber: used out += concatenation in a loop

Add `perms_valid` attribute to the `Encryption` class that stores the
result of `AlgV5.verify_perms()`. This allows callers to detect when the
`/Perms` integrity check fails for AES-256 encrypted documents (R5/R6),
indicating that the `/P` permissions field may have been tampered with.

Previously, a failed `/Perms` check only logged a warning with no
programmatic way to detect it.

Closes #3657.

Otherwise, applying a transformation to one of the pages renders all
pages referencing the shared objects invalid due to
`PageObject.replace_contents` setting them to a `NullObject` without
being able to reliable check for further usages.

Closes #3680.

## What's new

### New Features (ENH)
- Expose /Perms verification result on Encryption object (#3672) by @costajohnt

### Performance Improvements (PI)
- Fix O(n²) performance in NameObject read/write (#3679) by @dmitry-kostin
- Batch-parse all objects in ObjStm on first access (#3677) by @dmitry-kostin

### Bug Fixes (BUG)
- Avoid sharing array-based content streams between pages (#3681) by @stefan6419846
- Avoid accessing invalid page when inserting blank page under some conditions (#3529) by @j-t-1

[Full Changelog](6.8.0...6.9.0)