WIP: Native GPIO

- dummy and Linux sysfs GPIO drivers for native
- minor PIR driver test fix

TODO:
- [ ] add signal mode for sysfs driver
- [ ] implement writing for sysfs driver
- [ ] test sysfs driver on raspberry PI
- [ ] add control method for dummy interface
- [x] address sysfs GPIO availability issue
- [x] guard native system calls
- [ ] rename "dummy" to "virtual"?
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