OpenSystemsDevelopment / qpdf

Fix bug in #1595

- Standardize error handling by replacing repetitive throw statements with helper functions.
- Add test coverage for new helper functions in error handling.
- Enhance maintainability and readability with concise utilities.

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

- 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.

- 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

Utilize the GNUTLS_FIPS140_LAX around MD5 initialization.

…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.

…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.

… for clarity and consistency across dictionary operations.

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

…up method implementations, and simplify member handling.

…ed_ptr and forward declaration.

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

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

Simplify integer value retrieval by introducing a templated `value` method in the `Integer` class. Replace redundant exception handling logic across multiple functions with this unified approach. Streamline type conversions and improve readability.

…arameters with their existing empty values.

…e parameters with their existing values.

…ng handling with `qpdf::String`, and clean up `Members` class implementation.

…ant logic, and streamline type conversions.

…::types` helpers, simplify pipeline usage, and clean up includes.

… clean up unused file.

…and simplify pipeline logic.