Introduce LzmaEncoder and LzmaDecoder for raw LZMA1/LZMA2 encoding and decoding. This is the low-level complement to XzEncoder/XzDecoder (which handle the XZ container format) in #1542.

Some use cases require encoding or decoding raw LZMA streams without the XZ container, and need direct control over compression parameters (lc, lp, pb, dictSize). The existing XZ-level API hides these details behind presets and doesn't support raw encoding/decoding.