v2.58.0: EcuM68kDecoder: M68K/CPU32 decoder for GM P-series ECU firmware.** Wraps Capston

EcuM68kDecoder: M68K/CPU32 decoder for GM P-series ECU firmware. Wraps Capstone
(CS_ARCH_M68K / CS_MODE_M68K_020) with ECU-specific prologue scanning and pipeline-compatible
M68kInsn dataclass. CPU32 is a 68020 derivative; Capstone 5.0.7 has no CS_MODE_M68K_CPU32 but
020 mode decodes the GM P-series instruction set correctly.

• EcuM68kDecoder: disassemble() (Capstone-backed), decode_one(), function_starts() (pure scan), insn_length()
• M68kInsn: offset, mnemonic, op_str, insn_type, raw, size, target
• function_starts() primary signal: LINK.W A6, #-N (0x4E56 + negative 16-bit displacement); secondary: MOVEM.L regs, -(SP) (0x48E7) when not immediately after a LINK
• insn_type: RETURN (rts/rtd/rte/rtr), BRANCH (bra/b*/jmp), CALL (jsr/bsr), PROLOGUE (link.w A6 neg), MISC
• Branch targets strip Capstone .w/.l size suffix from $addr.w format
• disassemble()/decode_one() raise ImportError with install instructions when Capstone missing; function_starts() and insn_length() are pure-Python (no Capstone)
• Cs() constructed at __init__ time (not lazily) to eliminate thread-safety race
• 26 tests; FORGE gate: PASSED (0 findings)

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