New REL19/REL18 operand types + BRANCH_19/BRANCH_18 encodings + REL_PC19/
REL_PC18 relocations (R6 PC-relative semantics: offset is relative to the
instruction's own address, no delay-slot adjustment; LDPC aligns the PC
down to 8 and scales by 8). LWPC (mips32r6), LWUPC/LDPC (mips64r6).
Byte-exact vs llvm-mc and decode-clean; 281 tests green.
Each ISA's hand-written ENCODING_TABLE (the single source of truth) now lives
in a per-arch tablegen/ metaprogram that flattens it and serializes committed
binary blobs; the library #loads those into @(rodata) at compile time rather
than compiling a table body. No arch keeps encoding_table.odin or
decoding_tables.odin -- only a generated tables.odin loader and tables/*.bin.
* Two-stage, type-checked pipeline: tablegen Stage A emits human-readable
generated Odin, which compiles and serializes the blobs in Stage B.
* encode() goes through encoding_forms(m); decoders are unchanged apart from
x86's flattened 2-D index. Decode tables are byte-identical to the old ones.
* build.lua: a LuaJIT driver for the metaprograms, validations, and tests,
with cross-platform gating and a clear report.
* Docs refreshed; the obsolete forward-looking plan in cross_arch_design.md
trimmed to what was actually built.
* Attribution headers added to all rexcode source files; the generators emit
them so generated files keep them.
