Add experimental neutrobit reference kernel

[SeCuReDmE-main-dev]

Summary

• add an experimental backend-independent NeutroBit reference kernel under qumat/neutrosophic
• expose explicit three-state carrier normalization and qubit-subspace projection helpers
• add targeted kernel tests without changing production QumatCircuit behavior

Details

This is branch 2 of the experimental neutrosophic series anchored by apache/mahout#1372 and the docs foundation PR #1373.

This PR keeps the scope intentionally narrow. It introduces only the reference-state carrier and related helpers:

• NeutroBit over |0>, |1>, and |I>
• explicit normalization for the local three-state carrier
• measurement-probability extraction over the carrier basis
• projection into the qubit subspace for compatibility checks when the indeterminacy amplitude is absent

What this branch does not do:

• it does not modify QumatCircuit
• it does not wire neutrosophic execution into qiskit, cirq, or amazon_braket
• it does not introduce the gate family yet
• it does not claim native 3-state backend support

This keeps phase 2 focused on a clean experimental kernel that later branches can build on while remaining separate from the production backend surface.

Series anchors:

• RFC issue: RFC: Experimental neutrosophic operator layer for QuMat #1372
• Branch 1 PR: Add QuMat neutrosophic foundation docs #1373
• Previous branch in series: Add QuMat neutrosophic foundation docs #1373

Validation

• pytest testing/qumat/test_neutrobit_reference_kernel.py -q

RFC

• refs RFC: Experimental neutrosophic operator layer for QuMat #1372
• follows Add QuMat neutrosophic foundation docs #1373

[SeCuReDmE-main-dev]

Withdrawing this implementation slice from upstream review for now. To keep the discussion conservative and reviewable, we are limiting the public Mahout surface to the RFC issue and the Phase 1 docs PR while any further implementation branches remain protected on the fork side until maintainer feedback arrives.