[refactor](trx-rs): remove trx-ft8 C FFI crate, use trx-ftx directly

Delete trx-ft8 (C wrapper around ft8_lib + ft2_ldpc) and update
trx-server to depend on trx-ftx (pure Rust) directly. Removes
~2,900 lines of C code and all unsafe FFI.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

Cargo.lock

@@ -2642,14 +2642,6 @@ dependencies = [
  "trx-protocol",
 ]
 
-[[package]]
-name = "trx-ft8"
-version = "0.1.0"
-dependencies = [
- "cc",
- "libc",
-]
-
 [[package]]
 name = "trx-ftx"
 version = "0.1.0"
@@ -2712,7 +2704,7 @@ dependencies = [
  "trx-core",
  "trx-cw",
  "trx-decode-log",
- "trx-ft8",
+ "trx-ftx",
  "trx-protocol",
  "trx-reporting",
  "trx-vdes",