Implement product
Move implementations of ViewTransform+BlitzView into new traits Impl

Traits: ViewTransform -> ViewTransforms, BlitzView -> BlitzViewImpl
Hide private method >> in BlitzView, adapt implementations
Implement toArray with efficient in-place swapping

Fix Dmitry version: sz should be size - 1 (index range, not size)
Rewrite tests to verify consistency with List operations
Fix implementation of toList_: combinator op was inversed
Fix tests: some views had duplicated elements

Tests now guarantee BlitzView has the same semantic as List
We test this has the same interface too
Rename toLong{ -> s}
Restructure tests, add more tests, add TODO