[PR] Exclude alternative missing values from horizontal regridding of regrid2

[lee1043]

Description

Exclude alternative fillValue or missing values (e.g., 1e20) from horizontal regridding process or regrid2, so they won't influence to the regridded field.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

If applicable:

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass with my changes (locally and CI/CD build)
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have noted that this is a breaking change for a major release (fix or feature that would cause existing functionality to not work as expected)