NIF-based Prometheus text format parser.

Parses the entire Prometheus exposition body in a single NIF call, returning {entries, error_count} where entries is a list of {metric_name, labels_proplist, value, timestamp} tuples.

Lines without timestamps use 0 as sentinel.

Backed by the Rust parser in native/tms_engine (it replaced an earlier C++ NIF). Entry binaries are zero-copy sub-binaries of body: they keep the whole body alive until garbage collected, so anything storing them long-term must :binary.copy/1 them first.