test(bios): integrate pinned BIOS read-protection baseline

Add --suite bios with hash-verified upstream files and the ARM evaluation checkpoint at 0x08000248. Preserve the r12=0 assertion, original BIOS boot, and all test bytes. Add synthetic adapter and CLI regressions.

On Darwin arm64 the public ROM fails test 1 in debug and release after 64 steps and 543 nominal cycles. Document that this tests protected reads of Nintendo firmware opcodes, not general BIOS service compatibility. Online and offline preparation agree; 39 Python tests pass. Core behavior is unchanged.

tools/prepare_gba_tests.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-"""Prepare a pinned public ARM, Thumb, or memory test outside tracked paths.
+"""Prepare a pinned public ARM, Thumb, memory, or BIOS test outside tracked paths.
 
 This adapter is original. Upstream sources, license, and ROM bytes are downloaded
 only to the requested local directory. They are not embedded in this repository.
@@ -15,7 +15,7 @@ from urllib.request import Request, urlopen
 
 ROOT = Path(__file__).resolve().parent.parent
 LOCKS = {suite: Path(__file__).with_name(f"gba-tests-{suite}.lock.json")
-         for suite in ("arm", "thumb", "memory")}
+         for suite in ("arm", "thumb", "memory", "bios")}
 MAX_FILE_BYTES = 1024 * 1024
 
 
@@ -64,7 +64,7 @@ def prepare(output, source=None, download=fetch, suite="arm"):
         files[name] = data
 
     # The source-defined eval label starts with m_vsync's register save. All
-    # failure exits set the result register (ARM/memory r12, Thumb r7).
+    # failure exits set the result register (ARM/memory/BIOS r12, Thumb r7).
     # Thumb tests switch back to ARM before eval. Success leaves the result zero.
     # Hash pinning is authoritative; these checks catch adapter-offset mistakes.
     pc = int(lock["completion_pc"], 16)