[idea] Implement a true card emulation system

[jlitewski]

As described in #3, the BigBuf card emulation looks to be a glorified buffer for card data. Kinda seems like a waste to me. Since I'm pulling all those "emulation" functions out of BigBuf into their own files, might as well implement a true card emulation system into the firmware.

[jlitewski]

Current idea is this:

cardemu is a 'standardized' set of functions that the firmware can use to manage and manipulate tag/card data. It'll always allocate 4kb of memory minimum from palloc, even though it may not use all of it.

To set it up, you'll pass some sort of construction function pointer into init_emulator(*function_ptr). That function pointer will set the function pointers to the other standardized functions that cardemu has. For instance, ISO-14443 cards have three different UID lengths, and it shouldn't be cardemu's job to manage all of that logic to get the UID, it should be the job of whatever we initialized cardemu with; All cardemu should be worried about is returning a struct or byte array of the UID when get_emu_uid() is called.