AMR.load and AMR.amr_to_string changes data during read in test/amr_examples

[quffaro]

amr_to_string appears to change data as its being read. This means that a test case (AMR.amr_to_string(AMR.load(ASKEModel, model_expr))) == modelrep will always fail. Here are two concrete observations of this issue:

1. "@" character is omitted on AMR.load
   Expected Call the argument of amr_to_string in the test case M. A substring of M.header should read:
   "...ASKE Model Representation: SIR [email protected]..."
   Observed The substring of M.header omits the "@" character:
   "...ASKE Model Representation: SIR Model0.1..."
2. A match case in amr_to_string erroneously interprets ODERecord as ODEList
   Expected The ODERecord is interpreted by the ODERecord match case and return "ODE_Record = ..."
   Observed The relevant substring in the output of amr_to_string has "ODE Equations" instead.

[lukem12345]

@quffaro Can you upload these examples as tests to some branch in this repo?