update latlon2utm & convert_proj_txt

[zhuabaguai]

No description provided.

[daohu527]

@zhuabaguai This pull request refactors the projection handling in the imap library to provide more flexibility by supporting custom projection strings (proj_txt) in addition to the default UTM-based projections. The changes primarily affect the proj_helper module and its usage in the convertor module.

Refactoring projection functions:

• Replaced the latlon2utm function with latlon2projected, which now supports custom projection strings (proj_txt) in addition to the default UTM-based projection.
• Replaced the utm2latlon function with projected2latlon, which supports inverse transformations using either a custom projection string (proj_txt) or the default UTM-based projection.

Updates to convertor.py:

• Updated the import statement in imap/lib/convertor.py to use latlon2projected instead of latlon2utm.
• Modified the convert_proj_txt method to use the new latlon2projected function, passing the proj_txt parameter for custom projections.

[zhuabaguai]

Test passed