Add a SWAP mapping object (i.e. `switch`)

[ericpan64]

Problem

When writing mappings, want something that emulates the logic of a switch statement / conditional branching. Maybe this could be an enum that the Mapper class (and other related classes) cleans up

Requested feature

from pydian.dicts import SWAP

some_mapping = lambda d: {
   "a": SWAP(get(d, 'some_field'), {
      1: "one", # Handle specific cases (anything hashable)
      2: "two",
      str: "Got a str", # Handle classes
      None:  None # Handle base case
   }, strict=True) # Default strict -- expect developer to handle all cases
}

Alternatives considered

Additional context

• Fun to keep the 4-letter acronyms. SWAP ~ Switch with advanced positioning