Create a Testbench that tests calculated minimum fifo size

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Testbench flow:

• start writing as soon as possible
• start reading when data is not empty
• as soon as fifo full has been asserted finish the testbench since minimum fifo size was not properly calculated
• if all write bursts properly go through(no full assertion) minimum fifo size is good enough

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First attempt done in 2559f945032215d5b1477d3571941b9299a7ce74:

Noticed things:

• equation does not match the testbench
  • case 1: synchronous FIFO, bigger size of the FIFO is usually required
• it's problematic not to be able to set a FIFO_SIZE equal to not a power of 2

Things to improve:

• still did not do #2
• make the testbench more easily parametrizable

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Testbench works well in the synchronous fifo case(single clock domain), in the case of different frequency values it goes to shit, I don't yet know why

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Fixed some async + sync issues in #6, this version of the TB is good enough to use in my opinion