feat: support byte[] keyset columns

[DrSkillIssue]

Adds byte[] as a first-class keyset column type. Previously the cursor codec didn't know about it, and even if you got past that, the spine reconstructor only handled instance comparators with one argument, so a static byte[] comparer was structurally unrepresentable.

Three things had to move:

• TypedCursorIo + CursorWriter/Reader learn byte[] (varuint length + raw bytes).
• FilterPredicateStrategy gets a byte[] entry pointing at a static comparer that uses unsigned span comparison. MakeComparisonExpression now picks the instance-or-static Expression.Call form based on the MethodInfo, so the existing string/Guid/bool entries are unchanged.
• SpineReconstructor learns to flatten static 2-arg method calls, treating arg[0] as the entity side and arg[1] as the placeholder.