C API: add rocksdb_delete_range_cf_with_ts for user-defined timestamps

Start with include/rocksdb/c.h and compare the existing rocksdb_delete_range_cf and rocksdb_delete_cf_with_ts declarations. Then inspect db/c.cc and db/c_test.c for their corresponding implementation and timestamped-delete test patterns. Done means the new entry point forwards the timestamped range deletion, the C test covers it, and the unreleased_history note is updated.

Summary

The C API has no way to issue a range deletion with a user-defined timestamp. DB::DeleteRange has had a UDT overload (DeleteRange(const WriteOptions&, ColumnFamilyHandle*, const Slice& begin, const Slice& end, const Slice& ts)) on the C++ side for years, but the C API only exposes the non-timestamped rocksdb_delete_range_cf. There is no rocksdb_delete_range_cf_with_ts.

This leaves a gap for C and FFI consumers (e.g. the rust-rocksdb bindings): on a column family that enables user-defined timestamps, you can issue timestamped point deletes (rocksdb_delete_cf_with_ts, rocksdb_singledelete_cf_with_ts) but you cannot issue a timestamped range delete at all.

Background

The original UDT C-API work (#9889 / #9914) added timestamped Get, MultiGet, Delete, and SingleDelete, but did not include range deletes. This issue tracks completing that surface with the one missing entry point.

Proposed API

extern ROCKSDB_LIBRARY_API void rocksdb_delete_range_cf_with_ts(
    rocksdb_t* db, const rocksdb_writeoptions_t* options,
    rocksdb_column_family_handle_t* column_family, const char* start_key,
    size_t start_key_len, const char* end_key, size_t end_key_len,
    const char* ts, size_t tslen, char** errptr);

A thin forwarder to the existing C++ overload, modeled exactly on rocksdb_delete_cf_with_ts (for the Slice(ts, tslen) + SaveError pattern) and rocksdb_delete_range_cf (for the begin/end key plumbing).

Environment

• RocksDB: main (also reproduces on the 11.x releases)
• C API header: include/rocksdb/c.h

I have a patch ready (header declaration, db/c.cc implementation, a db/c_test.c case covering write-at-ts then delete-range-at-later-ts then read-at-later-ts, and an unreleased_history note) and am happy to open a PR.