Add symmetry-free MPS network to Hubbard and Ising models

[Copilot]

MPS (Matrix Product State) was available as a network architecture but not wired into the Hubbard or Ising model registries. Since MPS carries no symmetry constraints, it registers as "mps" (no /u1 or similar suffix).

Changes

• qmp/models/hubbard.py — adds MpsConfig with virtual_dim (bond dimension, default 16); uses sites = m × n × 2 to account for spin-up/spin-down orbitals per lattice site
• qmp/models/ising.py — adds MpsConfig with virtual_dim (default 16); uses sites = m × n

Both register under Model.network_dict["mps"].

Usage

# Hubbard 4×4, MPS bond dim 32
{"model": "hubbard", "model_config": {"m": 4, "n": 4}, "network": "mps", "network_config": {"virtual_dim": 32}}

# Ising 4×4 ZZ, MPS bond dim 16 (default)
{"model": "ising", "model_config": {"m": 4, "n": 4, "zh": 1}, "network": "mps"}

Original prompt

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This section details on the original issue you should resolve

<issue_title>将mps网络添加到hubbard和ising中</issue_title>
<issue_description>注意这个是无对称性的ansatz, 所以直接称呼为 "mps" , 不需要 "/u1" 之类的后缀</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes 将mps网络添加到hubbard和ising中 #211

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[Copilot]

Pull request overview

Wires the existing symmetry-free MPS network into the Hubbard and Ising model registries under the "mps" key.

Changes:

• Add MpsConfig (with virtual_dim) and register it as Model.network_dict["mps"] for Ising.
• Add MpsConfig (with virtual_dim) and register it as Model.network_dict["mps"] for Hubbard.
• Use sites = m * n (Ising) vs sites = m * n * 2 (Hubbard, spin up/down orbitals).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
qmp/models/ising.py	Imports MPS wavefunction, adds MpsConfig, and registers "mps" network for Ising.
qmp/models/hubbard.py	Imports MPS wavefunction, adds MpsConfig, and registers "mps" network for Hubbard (with * 2 sites).

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