chore: 适配vpn和代理

[fly602]

1、增加代理变化信号
2、当IP全为空时，自动设置代理为None

Issue: linuxdeepin/developer-center#9710 linuxdeepin/developer-center#9711

[deepin-ci-robot]

deepin pr auto review

关键摘要:

• 在initProxyGsettings函数中，新增代码逻辑可能存在逻辑错误，应确保当所有代理设置都为空时才设置代理模式为proxyModeNone。
• getProxyChildSettings函数中，错误信息err = fmt.Errorf("set proxy method through gsettings failed")应更具体，以清晰表达未成功设置代理方法的原因。
• setProxyMethod函数中，新增代码m.service.Emit(m, "ProxyMethodChanged", proxyMode)可能需要检查m.service是否为nil，以避免潜在的空指针异常。

是否建议立即修改:
是

[fly602]

/merge

[deepin-bot]

This pr cannot be merged! (status: unstable)

[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: fly602, zsien

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