Flush sealed head chunks to ULID-named block directories on disk. Each
block contains CRC'd chunk segment files (mmap'd for reads), a binary
index (symbol table, series, postings with TOC), and a meta.json written
last as the immutability gate. WAL is truncated after block fsync,
preserving the crash-safety ording invariant.
Bitstream primitives (bstream) and XOR encoder/decoder following the
Prometheus TSDB variant of the Gorilla scheme. Delta-of-delta timestamps
with 14/17/20/64-bit buckets, XOR-compressed float64 values. Decoder is
total: arbitrary bytes produce values or ErrShortStream.
david