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This prevents all wokers to send at once.

The grid reduction, grid fft and grid redistribution only needs to take
place once, after all the visibilities (in time) are processed. While
the order of operations is not completly corresponding to a real imager,
the number of times each operation is executed is.

Idg cal jakob 1 (rebased)

See merge request !51

Idgcal pyfixes

See merge request !52

Apply lm shift in wtiling

See merge request !50

This prevents slow initialization of m_wtiles_buffer.

set_grid(...) is already called at BufferSet level
Setting the grid before each (de)gridding call is not needed
and might interfer witch caching strategies such as w-tiling
employed by the Proxy.