Fix Size Calculation

[CascadingRadium]

• Fix Size() calculation to account for dynamic entries of the struct, to ensure that accurate information is passed on to the memory throttler

[abhinavdangeti]

@CascadingRadium would you throw in a detailed description and a much better commit header on what's exactly being addressed here and why.

[CascadingRadium]

I noticed a few structs had incorrect Size values due to some of the its fields not being accounted for...i fixed them to account such fields, like for example

1. len(string) should be there in the sizeOfBytes calculation because reflect.SizeOf will only incorporate the size of empty string -> vectorOptimizedFor and vectorSimilarity.
2. For numeric and datetime fields the PrefixCoded value, (a []byte), was not accounted for in the Size Calculation because of which the lastDocSize in Batch was slightly off since it did not include the length of the PrefixCoded value