[#720] Various parser fixes

Description

See individual commits.

Some notes:

There is a lot of weirdness around macros and braces in octez-client. It seems the reference parser either substitutes macros on the fly, or first parses to some very generic representation and then tries to fit it into a more concrete type. Either way, our setup is rather different, which leads to a lot of awkwardness. I tried my best to match, but this is a losing battle.

Long story short, with instructions that accept sequences of instructions as arguments, reference parser accepts either brace-wrapped sequences or macros that expand to sequences. If a macro consists of more than one token (e.g. IF {} {} as opposed to FAIL), then apparently it can be wrapped in parentheses.

Additional effort had to go into differentiating between MACRO and {MACRO}, which is in fact non-trivial since our types accept sequences of instructions and not singular instructions (which is correct, except macros work differently).

At this point, I wonder whether we should just make our parser as permissive as possible wrt braces and be done with it.

Related issue(s)

Resolves #720 (closed)

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