Implement RDB File Reading on Startup

[proXDhiya]

Implement functionality to read an RDB (Redis Data Persistence) file at the start of the program. The file will be provided via --dir and --dbfilename options. If the specified RDB file does not exist, the program should treat the database as empty.

Requirements:

• On program start, check if the RDB file specified by --dir and --dbfilename exists:
  • If the file exists, read and load the database from it.
  • If the file does not exist, initialize the database as empty.
• Implement support for reading numbers stored in the RDB file using both little-endian and big-endian formats, as per the RDB specification.
• Integrate the reading functionality with the SAVE command to ensure that a valid RDB file is generated and can be read back correctly.

Acceptance Criteria:

• The program correctly reads an existing RDB file at startup, loading the database with its contents.
• If the RDB file does not exist, the program initializes with an empty database.
• The program can correctly interpret numbers stored in little-endian and big-endian formats within the RDB file.
• The RDB file generated by the SAVE command is valid and can be successfully read on subsequent startups.

Additional Notes:

• Refer to the MDN article on endianness to understand how to handle little-endian and big-endian formats.
• Ensure the implementation is robust, handling edge cases such as corrupted or partially written RDB files.