Refactor as lib

[nitram509]

fix issue #61

• switch to Go 1.22
• separate the code to have separe CLI and library distribution in the same codebase
• introduce example code

---

TODO

• fix login copies session key into the session object
• add examples for all public methods
• add documentation for all public methods

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 30.03802% with 368 lines in your changes missing coverage. Please review.

Project coverage is 36.77%. Comparing base (a2528f0) to head (6cdffd9).

Files	Patch %	Lines
pkg/ntgrrc/port_set.go	31.94%	98 Missing ⚠️
pkg/ntgrrc/poe_cycle.go	0.00%	34 Missing ⚠️
pkg/ntgrrc/print.go	62.66%	28 Missing ⚠️
pkg/ntgrrc/poe_set_power.go	40.47%	25 Missing ⚠️
cmd/ntgrrc/login.go	0.00%	24 Missing ⚠️
pkg/ntgrrc/poe_settings.go	55.55%	23 Missing and 1 partial ⚠️
cmd/ntgrrc/poe_set_power.go	0.00%	21 Missing ⚠️
cmd/ntgrrc/port_set.go	0.00%	19 Missing ⚠️
pkg/ntgrrc/login.go	0.00%	13 Missing ⚠️
cmd/ntgrrc/poe_cycle_power.go	0.00%	11 Missing ⚠️
... and 14 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #62      +/-   ##
==========================================
- Coverage   39.27%   36.77%   -2.50%     
==========================================
  Files          18       29      +11     
  Lines        1184     1267      +83     
==========================================
+ Hits          465      466       +1     
- Misses        699      774      +75     
- Partials       20       27       +7     

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