chore(aztec-nr): extract per-signature calldata unpack helpers to shrink public_dispatch

[vezenovm]

Summary

Additional work towards resolving AztecProtocol/aztec-nr#35

• In generate_public_dispatch, count parameter-type signatures across the contract public functions. When at least EXTRACTION_THRESHOLD (4) functions share a signature, emit one #[inline_never] __aztec_nr_internals__unpack_arguments_<N> helper that does the calldata_copy + per-parameter stream_deserialize once, and rewrite those dispatch arms to call it.
• Signatures below the threshold keep the previous inline shape, so we do not pay CALL/RET overhead on call sites that would not recoup it.
• Follows the same pattern as chore(aztec-nr): mark emit_event_in_public as #[inline_never] to shrink public dispatch #23161, but targets the calldata-deserialization boilerplate the dispatch macro inlines into every arm rather than user-written helpers.

Bytecode impact

Measured via nargo compile --inliner-aggressiveness 0 + bb aztec_process, reading public_dispatch packed bytecode:

Contract	Baseline	Post	Δ
public_fns_with_emit_repro_contract	4,601	4,227	-374 (-8.1%)
avm_test_contract	51,333	51,048	-285 (-0.55%)

The repro contract is the same one used in #23161, so the delta stacks on top of that one. Real contracts with many public functions sharing parameter shapes is where we see savings from this change.

Additional Context

• The threshold is a single share-count knob for now. The real break-even depends on per-site stream_deserialize size (one Field arg vs. e.g. (AztecAddress, U128, PartialUintNote)), but a single threshold keeps the macro readable; we can size helpers against per-site savings later if needed.
• Follow-up: F-675 tracks centralizing validation for aztec-nr macro-generated internal names. The generated-name collision class predates this PR, and the new unpack helper names are one specific instance.