Change MultiSiteOperator function name to multisite_operator

[albertomercurio]

Description

I change the name of the MultiSiteOperator function to multisite_operator, since functions are always lower case here. Only structs can have upper case names.

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 93.68%. Comparing base (2b6e0d6) to head (f0ff205).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/deprecated.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #394      +/-   ##
==========================================
- Coverage   93.71%   93.68%   -0.04%     
==========================================
  Files          45       45              
  Lines        2896     2897       +1     
==========================================
  Hits         2714     2714              
- Misses        182      183       +1     

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[ytdHuang]

Would it be even easier to just name it as multisite (without _operator)?

[albertomercurio]

It can be misleading as ve could also have in the future the equivalent of multisite state

[ytdHuang]

It can be misleading as ve could also have in the future the equivalent of multisite state

ok, I see