Trace selectors

[denismerigoux]

In order to implement #657, a method for setting break-points will be needed, but also a method to inspect the trace and look at specific events quickly and easily. This need will also appear for explaining a computation to the end-user, as discussed in https://inria.hal.science/hal-04391612.

The trace is made up of raw events parsed into a tree data structure that is effectively the call tree of the Catala computation :

catala/runtimes/ocaml/runtime.mli

Lines 195 to 217 in 6e5e99a

	type event =
	| VarComputation of var_def
	| FunCall of fun_call
	| SubScopeCall of {
	name : information;
	inputs : var_def list;
	body : event list;
	}
	and var_def = {
	pos : source_position option;
	name : information;
	io : io_log;
	value : runtime_value;
	fun_calls : fun_call list option;
	}
	and fun_call = {
	fun_name : information;
	fun_inputs : var_def list;
	body : event list;
	output : var_def;
	}

In order to explore and filter this data structure, a specification language of tree nodes and leaves selector should be implemented. This way, we can try to match "all definitions of variable x inside a scope Foo being called underneath the subscope bar of scope Baz".