OpenSystemsDevelopment / qpdf

…with encapsulated `Config`, replace `qcf` with `d_cfg` for improved consistency, and adjust related logic for maintainability.

…` methods, update usage across codebase, and streamline related logic.

…input_entry`, centralize input file handling in `infile_name`, update `new_selection` logic, and simplify page range and input processing.

…, replace redundant file warning logic in `handlePageSpecs`, and simplify resource management.

…page_heap` and `page_spec_qpdfs`, simplify file handling, and improve code clarity.

…n` method, and update logic for handling page specifications.

…parameter, return success status, and streamline warning handling logic.

…based structure for page mapping, improve indexing logic, and clean up redundant variables.

…minate redundant variables, and simplify underlay/overlay page handling logic.

…e number and index handling, update related logic accordingly.

…DFJob_private.hh`, streamline includes, and reduce header dependencies.

Replaced std::shared_ptr<char> with std::string for passwords in QPDFJob. This simplifies memory management and aligns the implementation with modern C++ standards, improving code readability and maintainability.

Replaced shared pointer usage with a plain std::string for passwords in PageSpec to simplify code and enhance readability. Updated relevant logic and function calls to align with this change, removing unnecessary shared pointer management. Updated TODO to reflect completion of this modernization step.

Replaced `std::shared_ptr<char>` with `std::string` for password fields to simplify memory management and improve clarity. Updated relevant method implementations and function calls accordingly. This change ensures more straightforward and safer password handling throughout the codebase.

Replaced raw shared pointers with std::string for `infilename` to improve simplicity and readability. Added a boolean `empty_input` flag to explicitly track empty input cases. Adjusted related logic and function calls accordingly for consistency.

Replaced shared_ptr<char> with std::string for `outfilename` in QPDFJob, simplifying its usage and reducing unnecessary memory management overhead. Updated related conditional checks and logic to align with the updated type. These changes improve code readability and maintainability.

Thanks to github user @cdosborn for the basic enhancement.

... to remove the /Root /StructTreeRoot and /MarkInfo entries.

Accept --file and --range as named parameters in additional to
allowing positional arguments. This is in preparation for adding
additional flags.

This commit contains only the manual changes. It is separated for
clarity. This commit would not pass CI because it lacks the automated
changes, which appear in the next commit.

Rather than adding yet another flag that is almost never useful on its
own, just have --remove-restrictions disable digital signatures. The
operations are still separate in the API.