feat: Stinespring dilation

[bjoernkjoshanssen]

Stinespring dilation theorem, finite-dimensional version.
One of the Top 100 Quantum Theorems from https://marcodavid.net/top100/

[github-actions]

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[jstoobysmith]

This is my fault, but one of the linters for PhyslibAlpha is broken - meaning it is not properly checking whether or not the file is correctly imported into ./PhyslibAlpha.lean. I've prepared a fix at #1193. But in the meantime - please can add

public import  PhyslibAlpha.QuantumMechanics.StinespringDilation

to ./PhyslibAlpha.lean. This will end up triggering a bunch of other linters; primarily that a lot of your definitions don't have doc-strings.

[bjoernkjoshanssen]

This is my fault, but one of the linters for PhyslibAlpha is broken - meaning it is not properly checking whether or not the file is correctly imported into ./PhyslibAlpha.lean. I've prepared a fix at #1193. But in the meantime - please can add

public import  PhyslibAlpha.QuantumMechanics.StinespringDilation

to ./PhyslibAlpha.lean. This will end up triggering a bunch of other linters; primarily that a lot of your definitions don't have doc-strings.

Sounds good, trying that! But I can't find a linter that picks up on the missing doc-strings, runPhyslibAlphaLinters has no comment about it.

[jstoobysmith]

Ok, so what you have is technically not wrong, but your file here is missing a @[expose] public section. This means that every result in your file is 'private' and that your definitions don't need doc-strings. Adding:

@[expose] public section

underneath your module doc-string will result in these been picked up in your linters.

You can:

1. either leave things as they are for now and I can merge,
2. or, add this line and fix the linters.

Which would you rather do?

[bjoernkjoshanssen]

(2) sounds best since it'll improve the document in a straightforward way.

[jstoobysmith]

Looks good to me now. Approved. Will merge shortly