refactor: use and enforce go fix

[phm07]

For a more detailed explanation of go fix, see https://go.dev/blog/gofix
Note: This replaces all uses of interface{} in our public API with any. This should not be a problem, since they are equivalent as per the Go docs: https://pkg.go.dev/builtin#any
Since we currently require Go 1.25 in go.mod and any has been available since Go 1.18, this does not force a Go upgrade for consumers.

[codecov]

Codecov Report

❌ Patch coverage is 81.81818% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.39%. Comparing base (b5d4aa6) to head (acd2b4e).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
hcloud/rdns.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #848   +/-   ##
=======================================
  Coverage   78.39%   78.39%           
=======================================
  Files          60       60           
  Lines        4355     4355           
=======================================
  Hits         3414     3414           
  Misses        637      637           
  Partials      304      304           

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