feat(hid): recognise Nano receiver 046d:c534 (MK270, MK295) (#1456)

* feat(hid): recognise Nano receiver 046d:c534 (MK270, MK295)

The receiver-identity registry had no entry for USB product ID 0xc534,
the Nano receiver bundled with budget wireless combos such as the
MK270 and MK295, so OpenLogi never enumerated it or the paired
keyboard/mouse. Cross-checked against Solaar's NANO_RECEIVER_C534 as
the established reference implementation, alongside the neighboring
0xc537 Nano receiver already registered here.

Fixes #866

* test(hid): pin the new c534 receiver's exact identity mapping

receiver_identities_are_unique only proves no duplicate identity was
introduced; it says nothing about whether 0xc534 resolves to the right
brand and protocol. Adds a focused regression test alongside the existing
one for the c54d receiver.