Correct return types in Iuniswapv3poolstate Docs

[mivgubel]

I corrected the types in the Return Values table in the Documentation of the Iuniswapv3poolstate functions: positions & observations.

In positions function, I corrected the type of the _liquidity variable from bytes32 to uint128 to avoid confusion in the docs.

In observations function, I corrected the type of the blockTimestamp variable from uint256 to uint32 to avoid confusion in the docs.