feat(registers): self-describing config/frame registers

Add a BitField descriptor + Register base and per-IC config/frame
registers so opaque words decode themselves and build correctly:

- T5577Config          LF block-0 config word, mode-dependent data rate
- EM4100Code           64-bit frame + all parities (EM4102/EM4200 too)
- Type2Config          shared NXP CFG0/CFG1 base (auth0/prot/cfglck/authlim)
- Ntag21xConfig        + mirror / MIRROR_PAGE / NFC counter fields
- UltralightEV1Config  EV1 CFG0/CFG1
- UltralightCConfig    UL-C AUTH0 + AUTH1 protect scope
- MifareAccessConditions  per-block C1/C2/C3 -> English, inverted-copy
                          validation, build() that fills the inverted copy

Fields are documented attributes, so `<tab>` completes them in the shell
(bpython/ipython show each field's doc as the tooltip) and `repr` prints
the decode table. Bound to tags via `tag.config` / `tag.access(sector)`
/ `tag.code`. Bit layouts cross-checked against the firmware submodule
(cmdlft55xx, mifare4.c) and the NXP/EM datasheets. 40 new tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CLAUDE.md

@@ -57,6 +57,10 @@ pm3py/
     replay.py              # Trace replay
     access_control/        # Wiegand, OSDP
   transponders/            # tag/transponder models (extracted from sim/)
+    bitfield.py            # BitField descriptor + Register base — self-describing config
+                           #   registers (T5577Config, Ntag21xConfig, UL EV1/C, MFC access
+                           #   bits). Fields are documented attrs -> shell completion + repr
+                           #   decode table. Layouts cross-checked vs the firmware submodule.
     hf/iso14443a/          # Tag14443A_3/4, MifareClassic, DESFire, NfcType2/4
                            #   nxp/type2,ntag21x,ultralight,ntag_i2c
                            #   (NTAG210-216, Ultralight/C/EV1, NTAG I2C plus)