OpenSystemsDevelopment / qpdf

- Introduce distinct header guards to enable simultaneous inclusion of both headers.
- Update `README-maintainer.md` to document the changes .

Add `util::internal_error_if` for concise  handling of internal errors

- replace repetitive error handling with utility functions in BufferInputSource, OffsetBuffer, and QPDF_objects.

- Remove some "internal error" labels from errors that could be due to user logic errors.

Improve error handling for common PDF anomalies.

- Updated warning messages to provide clearer descriptions of common issues ("object has offset 0", "xref entry missing") and note that these are handled gracefully by qpdf.
- Adjusted logic in `QPDF_objects.cc` to identify and process `xref` stream-specific anomalies accurately.

Fixes #1594
Fixes #1292

Update release notes for #1587

Add detailed docstrings for main methods in `generate_auto_job`.

Enhance clarity and maintainability by introducing comprehensive (AI generated) docstrings for methods in the `Main` class, detailing functionality, parameters, and return types.

Utilize the GNUTLS_FIPS140_LAX around MD5 initialization.

Refactor: use local static variable for JSON schema in `initializeFro…

…remove unused global variable `JOB_SCHEMA`.

Since QPDFCrypto_gnutls is a short-lived object, it makes sense
to store the current FIPS mode value, set mode to LAX and restore
the original mode in the destructor.

If FIPS is not enabled the behavior should remain unchanged.

Fixes #1566.

Refactor QPDFFormFieldObjectHelper

…th `DV` and `default_value` methods. Simplify logic, improve clarity, and update references.

…lue` for clarity, consistency, and improved readability. Update references and method documentation accordingly.

…streamline logic, update references, and improve method documentation.

…ernativeName`, and `getMappingName` with streamlined implementations using `fully_qualified_name`, `partial_name`, `alternative_name`, and `mapping_name`. Simplify logic and enhance consistency across methods.

…` with `FT` method, streamline logic, and update related references for clarity and consistency.

…le_string` method for clarity, consistency, and improved readability.

…for flexibility and consistency across FormField methods. Adjust related method implementations accordingly.

…ntation, and update references in `FormField` methods.

…consistency, and update QPDFFormFieldObjectHelper accordingly.

Refactor private-API dictionary methods

… for clarity and consistency across dictionary operations.

Remove implementation detail from QPDFFormFieldObjectHelper.hh

…tionary, modernize constructors, and clean up null handling logic.

…up method implementations, and simplify member handling.

…ed_ptr and forward declaration.

Add `nullify` method to `BaseHandle` for setting objects to a mutable…

Add private-API Null class

…ent and simplified temporary null management. Clean up unused test coverage markers.

…ent and simplified temporary null management. Clean up unused test coverage markers.