Rewrite NVRAM parsers in KaitaiStruct

[NikolajSchlej]

Fuzzing showed that the current NVRAM parser is prone to deadloops because of offset backtracking. Because data formats for all supported NVRAM types are fairly simple, I expect them to be expressible in declarative KaitaiStruct language.

Progress:

• [x] AMI NVAR: https://github.com/LongSoft/UEFITool/commit/7eb565d788d0ca115b1448224e8d51c5a52f2fc1
• [ ] TianoCore FDC (gEfiVariableGuid)
• [ ] TianoCore VSS2 (gEfiAuthenticatedVariableGuid)
• [ ] TianoCore VSS
• [ ] TianoCore FTW
• [ ] Apple VSS/SVS/NSS
• [ ] Intel Legacy VSS
• [ ] Apple Fsys/Gaid
• [ ] Phoenix FlashMap
• [ ] Phoenix EVSA
• [ ] Phoenix CMDB
• [ ] Phoenix SLIC PubKey
• [ ] Phoenix SLIC Marker
• [ ] Phoenix Intel Microcode

[NikolajSchlej]

A test file that breaks the current parser oom-da07474f9bcec134c8120957f419e6d6ed23c46a.zip

[NikolajSchlej]

TianoCore VSS: https://github.com/LongSoft/UEFITool/commit/318fdb7fa188a81db36939164f4e94190bc761a3