feat: allowed empty AMM levels

[cdummett]

Summary

Currently core rejects any AMM pool which does not provide at least one unit of volume between every tick in the AMM's range. PR updates spec with a new market parameter $allowedEmptyAmmLevels$ which defines the maximum size of a range in which an AMM is allowed to quote no volume. This range is measured in ticks.

As a guide of what this change means for mainnet markets, the below plot shows the value $allowedEmptyAmmLevels$ should be set to for the smallest commitment to be valid when the specific parameters are selected.

e.g. to allow $leverageAtLowerBounds=5$ for a $lowerBound$ offset 2% from the $basePrice$, $allowedEmptyAmmLevels\geq1600$

The PR also gives equations for calculating the best-bid / best-ask to avoid core iterating over the range to find the price at which an AMM provides at least one unit of volume.

Notes

• PR also corrects spec inaccuracy where it is stated the curve is recalculated based on the account balances. The curve is in fact fixed based on the commitment size - see commit f2b856539a24350baec3ad1093f72106e25b6705.
• with current core implementation rearranging formulas to allow the AMM estimation API to return the commitment size for required for a specific pool is not trivial, for now it is left as simply returning pool valid / not-valid.

[davidsiska-vega]

Suggested change

	n\cdot\Delta{p} \geq {p_u} - (\frac{L\cdot\sqrt{p_u}}{L + \Delta{P}\cdot \sqrt{p_u}})^2
	n\cdot\Delta{p} \geq {p_u} - \bigg(\frac{L\cdot\sqrt{p_u}}{L + \Delta{P}\cdot \sqrt{p_u}}\bigg)^2

[davidsiska-vega]

Suggested change

	this is equivalent to