Allocate temporary buffers in Network::init

[primenumber]

This PR is premise to solve #473 .
Make easier to manage memory.

Motivation and Context

This PR allocate temporary buffers which is used operators in Network::init.
Memory allocation only occurs in Network and debug routines (such as time_measurement).

Description

• Define unique_ptr in Network instead of global
• Stop to use std::vector in generic qconv operator.
  • This vector is used to manage threads, so changed to use OpenMP instead native threads.

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Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature / Optimization (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.

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This PR needs Approvals as follows.

• Ownership Approval for / from iizukak, tkng, ruimashita
• Readability Approval for Python from tkng, tsawada
• Readability Approval for C++ from tkng, tsawada

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/ready

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