[DEV] New feature: inline syntax

[MatrixEditor]

this pull request tracks changes related to the v2.8.1 release

Changes made here introduce a new inline syntax that can be used to unpack structs (not annotated struct classes) from bytes or a stream:

stream = BytesIO(b"\xff\xff@\xe2\x01\x00")

# To affect the endianess, either use 
O_DEFAULT_ENDIAN.value = LittleEndian
# or creating a constant field that represents the typed struct
uint32le = LittleEndian + uint32

# to read/unpack values from a stream/buffer, just use the left shift operator
value1: int = uint32le << stream 
value2: int = uint16 << stream 
value3: str = String(10) << stream 

---

Added

• New inline syntax using the << operator to automatically unpack structs from data
• All default struct types now implement from_bytes, from_file and to_bytes for direct packing or unpacking
• Add PackMixin and UnpackMixin to automatically implement the methods mentioned above for struct types

Changes

• pack, unpack and sizeof were moved into their own module (no changed visibe when importing from caterpillar.models)

Removed

• Drop support for 'x' format character in PyStructFormattedField

Fixes

• Pre-computed conditions in the Field class incorrectly evaluated to true or false unconditionally (in case of a context-lambda). This issue has now been fixed in all places.
• Fix some missing or wrong typing annotations
• Fix unpacking with dynamic offsets #57: allow dynamic offsets to be used again