Refactor Hcontainer-related codes: remove current_R in atom_pair.h

[mohanchen]

Refactor codes related to HContainer: remove current_R in atom_pair.h, as this mutable variable introduces potential OpenMP data races.

HContainer Refactoring Requirements
1. Current Problems
The HContainer class provides a set of member functions for external business calls. In actual usage scenarios, these functions often need to be invoked consecutively to complete a complete business operation. However, there are strict mandatory dependencies on the assignment order of internal variables between these sequential member functions.
Currently, such invocation constraints and variable assignment preconditions are only implicitly coupled inside the class, without explicit interface constraints, parameter checks, or unified process encapsulation. This leads to an extremely high threshold for external developers to use HContainer correctly. Only the original developer who implemented the internal logic of this class can fully follow the implicit execution order and avoid hidden pitfalls.
For other team members who call the HContainer interface, it is very easy to make mistakes such as disordered function invocation order and missing prerequisite variable assignments. These incorrect usages will cause abnormal business logic, inconsistent data status, and hard-to-reproduce hidden bugs, which greatly increases the difficulty of troubleshooting and subsequent maintenance costs.
2. Refactoring Objectives
The core goal of HContainer refactoring is to optimize interface usability and robustness, eliminate implicit calling dependencies, and make the component more developer-friendly:

• Hide underlying invocation logic: Encapsulate the internal strict variable assignment sequence and sequential member function calling logic, shield implicit underlying constraints from external callers.
• Unify external interface capabilities: Provide highly aggregated and integrated external interfaces, avoid fragmented multi-step manual calls by users, and reduce mental burden.
• Enhance fault tolerance and robustness: Add necessary state verification and parameter legitimacy checks inside the class to prevent logic errors caused by incorrect calling sequences.
• Reduce usage costs: Enable all developers to use HContainer correctly and stably without fully understanding the internal implementation details, eliminating exclusive usage barriers for original developers.

[ErjieWu]

This PR has removed the variable current_R from the internal part of HContainer class which is used to mark the Bravais vector of the current operation position. It has controlled all operations involving the Bravais vector through function parameters passed as arguments, which effectively avoids unnecessary variable dependencies and also enhances the stability during parallel processing.
LGTM.