Add loop and restBuffer types

[extremeheat]

Generated by Claude 4

loop

Reads a sequence of elements until a terminator or end of buffer:

// Read numbers until encountering 0
['loop', { type: 'i8', nt: 0 }]  // [1, 2, 3] from buffer [1, 2, 3, 0, ...]

// Read until end of buffer  
['loop', { type: 'i16', nt: null }]  // Read all remaining i16 values

restBuffer

Captures all remaining bytes as a Buffer:

// Protocol with header and payload
['container', [
  { name: 'header', type: 'u8' },
  { name: 'payload', type: 'restBuffer' }  // All remaining bytes
]]

After #169 , ProtoDef-io/ProtoDef#55