OpenSystemsDevelopment / qpdf

…fy logic, and enhance consistency with modern C++ practices.

- Introduced a `validate()` method in `QPDFNameTreeObjectHelper`, `QPDFNumberTreeObjectHelper`, and `NNTreeImpl`.
- Ensure proper validation of tree keys and values, detecting invalid entries, unsorted keys, and inconsistencies.
- Added support for auto-repair in case of validation errors.

- Introduced `std::function<bool(QPDFObjectHandle const&)>` to validate tree values.
- Updated constructors and methods across `QPDFNameTreeObjectHelper` and `QPDFNumberTreeObjectHelper` to support value validation.
- Refactored `NNTreeImpl` to check for invalid values during insertion, iteration, and retrieval.
- Improved error handling and reporting for invalid values.

- Introduced a new test case to verify handling of damaged page labels.
- Added expectations for incorrect tree order and non-dictionary value errors.
- Included output file and test PDF for validation.

Fix #1527

Improve null key/value handling in `NNTree`, add checks across insert…

Fixes bug in #1523

Validate existence of array items in `NNTree`, improve null handling,…

Fixes bug in #1523

Refactor private API class Array

… checking, and align with `Array` API conventions.

…prove bounds checking

…y, modify bounds checks, and adjust affected tests.

… to use subscript operators, and simplify object access logic.

…bounds checks with subscript operator, simplify loop logic, and remove redundant trace.

…hecks with `Array` subscript operator, simplify logic, and improve null handling.

…rray`, use subscript operators, simplify logic, and improve readability.

…s`, remove redundant trace, and improve null handling.

…move redundant trace, and improve readability.

…reamline object assignment, and introduce constructors for `QPDFObjectHandle`.

Add private-API subscript operators to `QPDFObjectHandle`

…tem` with `size` and subscript operators, simplify logic, and improve error handling.

…ems` and `getArrayItem` with `size` and subscript operators, and improve code readability.

…ms` and `getArrayItem` with `size` and subscript operators, remove redundant debug traces, and improve readability.

…em` with `size` and subscript operators, remove redundant debug traces, simplify loop logic, and improve readability.

…` and subscript operators, remove redundant debug traces, and improve code readability.

…eplace `getArrayNItems` with `size`, and improve error handling logic.

…Items` with subscript operators, introduce `std::cmp` utilities, and remove redundant debug traces.

…logic, and replace redundant code with subscript operators.

…lify `withinLimits` logic, and improve code readability with subscript operators.

…` and `getArrayNItems` with subscript operators for readability and cleaner syntax.

…edundant debug traces.

…and improve `findInternal` readability.

Implement subscript operators (`operator[]`) to provide indexed access to `QPDFObjectHandle` for both `size_t` and `int` types.

Add error handling for missing or invalid Resources and invalid or du…