fix: Zero index is not always 0

[Sarkoxed]

This pr changes the export method of circuit builders, adding the name "zero" to an appropriate index, which is not always 0.

[github-actions[bot]]

Changes to public function bytecode sizes

Generated at commit: 42b28d0611d67c0f81301c77cf98dc19a9b9f085, compared to commit: 133384c8234c79b11488578c6a1520b3de4fda79

🧾 Summary (100% most significant diffs)

Program	Bytecode size in bytes (+/-)	%
AvmTest::public_dispatch	-735 ✅	-1.21%

---

Full diff report 👇

| Program | Bytecode size in bytes (+/-) | % | |:-|-:|-:| | **AvmTest::public_dispatch** | 60,027 (-735) | **-1.21%** |