Complete the Roaring64 C++ API

#840 added a C++ Roaring64 class wrapping the ART-based 64-bit C API, only covering a core subset of functionality. This issue tracks the rest of the API surface.

Each item below here maps to an existing C function in roaring64.h.

Checked/range operations:

• addChecked / removeChecked
• addRange / addRangeClosed
• removeRange / removeRangeClosed
• containsRange / containsRangeClosed

Predicates:

• isFull
• isSubset / isStrictSubset

Flip:

• flip / flipClosed

Optimization:

• removeRunCompression / runOptimize / shrinkToFit

Rank/select:

• rank / select / getIndex

Serialization:

• write / getSizeInBytes / read / readSafe
• frozenView / writeFrozen / getFrozenSizeInBytes

Misc:

• fastunion
• uint32_t convenience overloads

Start with the C++ Roaring64 wrapper added in #840 and compare its existing API with the corresponding declarations in roaring64.h. Work through the unchecked groups, using the existing C functions as the behavior reference. Done means the remaining listed operations, frozen serialization methods, fastunion, and uint32_t overloads are exposed consistently with the completed methods.