Add CFG transformation interface with loop unrolling

[giacomozanatta]

Description
Adds a pluggable CFGTransformation extension point in lisa-sdk, applied per-CFG between program finalization and the fixpoint, and LoopUnrolling as the first concrete transformation.

Loops are unrolled by unwinding the first k iterations of each innermost Loop as straight-line clones in front of a residual copy of the original loop.

Further content

**Demo (test conditionalCounter)

(y = 0; while (x < 100) { if (x == 90) y = 42; x++; }; return y;) with interval analysis:

config	return y
baseline	[0, +∞]
unroll-2	[0, +∞]
unroll-4	[0, +∞]
unroll-100	[42, 42]

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