Add wrappers for the standard input, output, and error streams

[dreamer-coding]

Fossil XSDK Pull Request

Description

This change introduces fossil_fstream_t wrappers for the standard input, output, and error streams, defined as FOSSIL_STDIN, FOSSIL_STDOUT, and FOSSIL_STDERR. These are now declared as external fossil_fstream_t* pointers, replacing the previous direct mappings to stdin, stdout, and stderr. This provides a consistent and extensible abstraction over standard streams, aligning them with the rest of the fossil_fstream_ API for improved portability and stream management across platforms.

Testing

Same test to ensure everything works

Checklist

• Code follows the project's coding standards.
• Tests have been added or updated to cover the changes.
• Documentation has been updated to reflect the changes.
• The code has been reviewed by team members.
• All checks and tests pass.
• The license header and notices are updated where necessary.

License

This project is licensed under the Mozilla Public License - see the LICENSE file for details.