Code simplification

[andrijamitrovic23]

Involved artifacts

• blobstream-contracts/src/lib/tree/namespace/TreeHasher.sol

Description
NMT assumes that the leafs are ordered by namespace. This assumption is not used here as it is used in the rest of the code.

Problem Scenarios
Findings listed above could not introduce any issues, they are suggestions for code improvements.

Recommendation
Calculated minimum namespace is always equal to the left minimum namespace so it could be calculated as follows:
Namespace memory min = l.min

This is how it is done in the nmt library that is used in Celestia:
minNs := leftMinNs