Correctly account for Cr and Cb subsampling for native YBR_FULL_422

[CPBridge]

Addresses #235

Occasionally the YBR_FULL_422 photometric interpretation is used for native encoded pixels. When this occurs, the calculation of bytes per frame needs to account for the subsampling of the colour (Cr and Cb) channels. The logic is given here as:

Rows (0028,0010) * Columns (0028,0011) * Number of Frames (0028,0008) * 2

This seems to work correctly with the sample file shared in #235.

[CPBridge]

Note that tests are currently failing for reasons unrelated to this PR, see #243 . We should wait on #244 before proceeding with this PR

[CPBridge]

Note that issues #235 and #241 seem to be resolved by this change. However, there is more to think through before merging:

• Dealing with the other subsampled photometric interpretations
• Adding tests
• Performing colour space conversion to RGB when colour correction is requested

[CPBridge]

Added a test and pushing this out so that it makes it into the next release (0.22.0). I will try to fix the colour space issue soon, but for now users can retrieve the frames without colour correction and then use eg pillow to convert YBR to RGB

[CPBridge]

Merging, since tests are failing for reasons unrelated to this PR