Refactor chunked matrix for accommodating memory-mapped utility module

[weiliw-amz]

Issue #, if available:
N/A

Description of changes:
Refactor chunked matrix in inference.hpp for PECOS XLinear model inference

• Concatenated original chunked matrix's fragmented memory allocation
  • For accommodating subsequent memory-mapped utility module.
  • This change increases time cost of making chunked matrix by 5%~10% for large models (>50G), but is necessary and cannot be avoided.
• Reduced memory footprint of making chunked matrix

Fixed type inconsistency in matrix.hpp.

Tested on large (~50-100G) XLinear models for result validation and time efficiency.

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