[orc-rt] Add SPSSequence serialization from iterator_range. (#207715)
Adds an SPSSerializationTraits specialization that serializes an
iterator_range<IteratorT> as an SPSSequence<SPSElementTagT>, matching
the wire format of the existing container and span sequence serializers.
The element type is deduced via std::iterator_traits, so both class-type
iterators and raw pointers are supported.
This lets callers serialize an arbitrary [begin, end) sub-range
directly, without first copying the elements into a temporary container.
Only serialization is provided: a bare iterator pair has no meaningful
deserialization target, so decode into a std::vector (or other sequence
type) as usual.
Please enter the commit message for your changes. Lines starting