feat: use custom IDOrName type for schemas

[jooola]

Add typing information to the fields that support passing either an ID as int, an ID as string or a Name as string. An empty value will be marshalled to null to reflect the behavior of an empty interface.

After this change, we do not have to cast IDs to float64 or to string to be able to read the values.

Since this is part of the schema package, this is not a breaking change for our customers, but might break our tests that rely on casting the interface to the desired type.

[codecov]

Codecov Report

Attention: Patch coverage is 94.44444% with 3 lines in your changes missing coverage. Please review.

Project coverage is 68.08%. Comparing base (9903f4d) to head (4b6096f).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
hcloud/schema/id_or_name.go	92.50%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #545      +/-   ##
==========================================
+ Coverage   67.71%   68.08%   +0.36%     
==========================================
  Files          46       47       +1     
  Lines        4882     4900      +18     
==========================================
+ Hits         3306     3336      +30     
+ Misses       1166     1158       -8     
+ Partials      410      406       -4     

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[apricote]

Nice cleanup!