Refine Div CPU implementation

[jysh1214]

The Cytnx arithmetic implementation contained lots duplicated code across different type combinations, which caused:

• Difficult maintenance when updating logic
• Low code readability due to repetitive patterns

This PR refines the Div CPU implementation, similar to #651.
Our goal is to generalize all arithmetic operations using templates, and eventually refactor the multiple-dispatch mechanism for arithmetic.

template <typename TLin, typename TRin>
void ArithmeticInternalImpl(...) {
  if (type == 0)
    cytnx::linalg_internal::AddInternalImpl<TLin, TRin>(
      out, Lin, Rin, len, shape, invmapper_L, invmapper_R);
  else if (type == 1)
    cytnx::linalg_internal::MulInternalImpl<TLin, TRin>(
      out, Lin, Rin, len, shape, invmapper_L, invmapper_R);
  else if (type == 2)
    // ...
  else
    // ...
}

Next, we plan to replace the linalg_internal::lii.Ari_ii usage in arithmetic .cpp files with the std::variant + std::visit pattern, similar to what we did in commit 710c98c.

This is the last PR for Arithmetic OPs.

[codecov]

Codecov Report

❌ Patch coverage is 12.18487% with 209 lines in your changes missing coverage. Please review.
✅ Project coverage is 34.97%. Comparing base (be1cfcf) to head (282f955).
⚠️ Report is 78 commits behind head on master.

Files with missing lines	Patch %	Lines
...ackend/linalg_internal_cpu/Arithmetic_internal.cpp	11.00%	186 Missing ⚠️
src/backend/linalg_internal_cpu/Div_internal.hpp	20.68%	21 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #715      +/-   ##
==========================================
+ Coverage   32.07%   34.97%   +2.89%     
==========================================
  Files         215      215              
  Lines       36242    32974    -3268     
  Branches    14543    13142    -1401     
==========================================
- Hits        11626    11532      -94     
+ Misses      22692    19544    -3148     
+ Partials     1924     1898      -26     

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