feat(quantum-mechanics): mulOperator domain and add/sub

[gloges]

• Adds lemmas for (𝓜 μ f).domain = ⊤, (𝓜 μ f).domain ≤ (𝓜 μ g).domain and (𝓜 μ f).domain = (𝓜 μ g).domain (and corresponding MemHS properties).
• Proves 𝓜 μ f is closed.
• Adds a new sufficient condition for 𝓜 μ (f ± g) = 𝓜 μ f ± 𝓜 μ g.

[github-actions]

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