Add memory and core estimate function

[FedeMPouzols]

Resolves #263.

This adds the function estimate_conversion_memory_and_cores() to convert_msv2_to_processing_set.
A simple example is added to the ps_vis tutorial (tried to keep this as short as possible to prevent loss of focus on the MSv4).
The estimates seem reliable enough, with two caveats:

• MSv2s with large pointing tables relative to main table => will tend to underestimate
• There is currently a ~5-6% overestimation to cover for that plus other possible buffer allocations in to_zarr()

I'd suggest we follow-up on this with an issue to add memory estimates of pointing and sys_cal. That would make it possible to have a more precise model and reduce the overestimation.

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Note well:

This contribution is made under the current ALMA software agreements. 
(c) European Southern Observatory, 2024 
Copyright by ESO (in the framework of the ALMA collaboration)

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