libxml-rs 0.1.0-alpha.11

Phase 9: EXSLT + xsltproc. Native-Rust forensic reimplementation of libxml2+libxslt with C ABI drop-in replacement. Complete EXSLT (exsl:node-set on RTFs, math, sets, strings, dynamic, dates, functions), full xsltproc CLI with upstream exit codes, byte-identical differential parity against libxslt 1.1.45 across a 12-case corpus, 1110 tests passing, XSLT 1.0 engine + all prior surfaces.