core-clp: Refactor `LibarchiveFileReader` to properly handle empty data blocks (fixes #389).

[LinZhihao-723]

Description

The current LibarchiveFileReader implementation has the following problems:

• It doesn't handle the case where the data block is empty, which is the root cause of #389
• Not all data members are initialized in the default constructor
• Buffer peeking method's signature can be improved with C++20 enabled

This PR makes the following changes accordingly:

• Handle the empty data block properly. All empty blocks will be skipped and only nonempty blocks can be read
• Initialize all data members in the member declaration (which matches our latest coding guideline)
• Using std::span for peeking buffer content

Validation performed

• Ensure CI passed
• Ensure the bug has been fixed in #389