Melt windows fix

[TomMelt]

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fixes #124

This is currently wip. It needs to be tested by end user.

If this fixes the problem I will tidy up the int64 issue and we can merge this PR in.

Tasks:

• [x] fix cmake windows build issue
• [ ] fix int64 issue properly

[jatkinson1000]

Discussion:

• For the places we have integer types we replace by an explicit int32.
• This will remove the issues on Windows where we get a mismatch.
• Ensure docs are updated to be clear users now need to specify the type of int.
• This will allow this to be closed, and relates to #124 and #140

[TomMelt]

This all looks reasonable and in agreement with what we discussed in the meeting, thanks!

The remaining thing to do is to document this, as mentioned in the checklist for the PR.

thanks. Just done in https://github.com/Cambridge-ICCS/FTorch/pull/137/commits/d64358c7cb5d3a6c0c2427b1168a96d05cd01e94

[TomMelt]

the only test that fails is in the static analysis when running fortitude. This will be fixed separately by #205