Refactor: only keep one `Charge_Mixing::inner_product_recip()`

[WHUweiqingzhou]

Describe the Code Quality Issue

Currently, ABACUS has three functions to calculate the inner product of two vector in recip space, namely:

1. Charge_Mixing::inner_product_recip()
2. Charge_Mixing::inner_product_recip_new1()
3. Charge_Mixing::inner_product_recip_new2()

Too many similar functions will confuse others.
Since the data stored in rhog is not what Charge_Mixing want, the input data of Charge_Mixing::inner_product_recip() and Charge_Mixing::inner_product_recip_new1() is different. I will:

1. move Charge_Mixing::inner_product_recip() and get_drho() into Charge
2. let all mix functions use Charge_Mixing::inner_product_recip_new1()

This is a step for refactor of Charge_Mixing class #3363.

Additional Context

No response

Task list for Issue attackers (only for developers)

• Identify the specific code file or section with the code quality issue.
• Investigate the issue and determine the root cause.
• Research best practices and potential solutions for the identified issue.
• Refactor the code to improve code quality, following the suggested solution.
• Ensure the refactored code adheres to the project's coding standards.
• Test the refactored code to ensure it functions as expected.
• Update any relevant documentation, if necessary.
• Submit a pull request with the refactored code and a description of the changes made.