Add fetch_bignumeric attribute

[startork]

Related to #1498

Add in optional bignumeric attribute which converts sql bigints to php ints and sql decimal and numeric to php float

Add basic tests for string vs int/float returns

[startork]

Hi @v-makouz
Would you be able to give me some advice? I'm unsure whether to
a) Treat bigints as integers straight from the start, using c++ long long types or
b) to handle similar to datetime, keeping existing code as much as possible and only converting to int when required as a zval.

Thanks,
Starsky

[v-makouz]

I think treating it like datetime would be more straightforward. But I see there are still some automated test fails, like the "Numeric value out of range"