refactor: extract sniff infrastructure into pm3py/sniff/ sub-package

Phase 2 of package refactor. Extracts trace parsing, ISO 15693
decoders, NDEF annotation, and ANSI formatting from core/hf_iso15.py
into dedicated sniff/ modules:
- sniff/trace.py — parse_tracelog (protocol-agnostic)
- sniff/ndef.py — NDEF TLV/record decode
- sniff/decode_iso15.py — 15693 command/response decoders
- sniff/format.py — ANSI color formatting
- sniff/session.py — SniffSession with iso15() method

core/hf_iso15.py re-exports sniff symbols for backward compat.
Also fixes NTAG 5 placement (iso15693, not iso14443a4) in design doc.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/plans/2026-03-18-refactor-progress.md

@@ -45,8 +45,8 @@ Created `pm3py/sniff/__init__.py` placeholder. Will extract into sub-modules whe
 
 Created full directory tree per design:
 - `transponders/hf/iso14443a3/nxp/` — MIFARE Classic, Ultralight, NTAG
-- `transponders/hf/iso14443a4/nxp/` — DESFire, NTAG 5
-- `transponders/hf/iso15693/nxp/` — ICODE SLIX2
+- `transponders/hf/iso14443a4/nxp/` — DESFire
+- `transponders/hf/iso15693/nxp/` — ICODE SLIX2, NTAG 5
 - `transponders/hf/iso15693/st/` — ST25TV
 - `transponders/lf/atmel/` — T55xx
 - `transponders/lf/em/` — EM4100, EM4x05