Move all ten ISA packages (x86, arm32, arm64, mips, riscv, ppc, ppc_vle,
rsp, mos6502, mos65816) from core/rexcode/<arch> to core/rexcode/isa/<arch>,
so the import pattern is now `import "core:rexcode/isa/x86"`. The shared
core stays at core:rexcode/isa.
Mechanical: relative `import "../isa"` / "../../isa" -> absolute
"core:rexcode/isa" (the only path that survives the move; the "../" and
"../.." self/generated imports move with their packages). build.lua now
builds paths as <root>/isa/<name>; stale `cd <arch>` hints in the verify
tools and the doc.odin paths updated.
WASM stays at core/rexcode/wasm for now -- it is an IR, not an ISA, and
will move under the forthcoming core:rexcode/ir once that layer lands.
All 10 arches gen/builders/check/test green; import core:rexcode/isa/x86
verified working; wasm still compiles.
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.
