feat(QuantumMechanics): add DirichletSubmoduleOn

[gloges]

Adds submodules of the Space d Hilbert space on Ω consisting of Schwartz maps which vanish on frontier Ω = closure Ω \ interior Ω. These can serve as the domain for an operator which acts on wavefunctions satisfying Dirichlet boundary conditions (e.g. the Hamiltonian for the infinite square well).

• Basic.lean: defines SpaceDHilbertSpaceOn and reorganizes to add namespace and section variables.
• SchwartzSubmodule.lean: defines SchwartzSubmoduleOn as the projection of SchwartzSubmodule from SpaceDHilbertSpace onto SpaceDHilbertSpaceOn.
• DirichletSubmodule.lean: defines DirichletSubmoduleOn as the projection of a submodule of 𝓢(Space d, ℂ) and proves that it is contained in SchwartzSubmoduleOn.

[github-actions]

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[jstoobysmith]

This looks good to me. Approved :)