feat: add std::string_view overload for Symbol::For

[umuoy1]

Symbol::For had overloads for const std::string&, const char*, String, and napi_value, but was missing a std::string_view overload. This made it inconsistent with other APIs like String::New which already accept std::string_view, and forced users to convert std::string_view to std::string or const char* before calling Symbol::For.

Adding the std::string_view overload provides a more consistent API surface and avoids unnecessary string copies.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.65%. Comparing base (0add130) to head (cdece99).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1722      +/-   ##
==========================================
+ Coverage   63.61%   63.65%   +0.03%     
==========================================
  Files           3        3              
  Lines        2056     2058       +2     
  Branches      729      729              
==========================================
+ Hits         1308     1310       +2     
  Misses        162      162              
  Partials      586      586              

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