BitBox02 firmware

This commit fixes a typo-like bug in the BitBox02 hardware wallet's Ethereum transaction signing code. The firmware was supposed to reject a 'max_fee_per_gas' value that has an unnecessary leading zero byte, but it was accidentally checking 'gas_limit' instead. Leading-zero values can cause the device and a connected computer to compute different transaction hashes, which could let an attacker trick the user into signing one transaction while the computer broadcasts a different one. The fix corrects the field check and adds tests for both fee fields.

This commit is a pure code reorganization: it moves the BitBox02-specific hardware abstraction layer (HAL) implementation out of one large file into several smaller files in a new submodule. No functionality, behavior, or security properties of the firmware appear to change. It is comparable to rearranging chapters in a book without rewriting the text.

This commit is a simple code reorganization: it takes several related pieces of a hardware abstraction layer (HAL) that were all written in one large file and splits them into smaller, separate files. No behavior of the device or its security functions was changed. It is comparable to moving chapters of a book into individual files without rewriting the text.

This commit is a simple internal cleanup in the BitBox02 firmware's Rust code. It removes a shortcut (a 're-export') that made test-only user-interface helpers available under an old module path, and updates all test files to import those helpers directly from their new location. There is no change to the actual device behavior, no bug fix, and no security impact.

This commit is a pure internal code reorganization (refactor) of the BitBox02 firmware's Rust code. It moves the user-interface trait and its real/testing implementations into a new 'hal' (hardware abstraction layer) module structure and renames some types (e.g., Workflows -> Ui, RealWorkflows -> BitBox02Ui, TestingWorkflows -> TestingUi). No security-sensitive behavior appears to change; it is a maintainability/clean-up change.

This commit introduces a new asynchronous task engine into the BitBox02 firmware. It vendors third-party Rust libraries (async-task, concurrent-queue, crossbeam-utils) and adds a custom executor plus a small demo that shows an orientation screen and a delay. There is no indication in the commit message, diff, or supplied references that this change fixes or introduces a security vulnerability; it appears to be a routine architectural/feature addition.

This commit rewrites the BitBox02 hardware wallet's main firmware loop from C to Rust. It is a large refactoring change that moves core USB, Bluetooth/UART, and workflow handling into Rust. The change itself is not a security fix and does not introduce an obvious vulnerability in the diff, but any rewrite of security-critical firmware code carries a risk of subtle behavioral differences or memory-safety edge cases at the C/Rust boundary. The commit message and diff do not describe any security issue or credit a researcher.

This commit removes an empty placeholder function called hww_process() that did nothing. It is a routine code cleanup with no security relevance.

This commit is a build-system refactor: it moves the FatFs microSD filesystem library from a direct CMake target into a new Rust crate wrapper, and makes sure C compiler hardening flags (such as stack-protector) are also applied when Cargo's build.rs scripts compile C code. There is no obvious runtime vulnerability in the diff, but the change touches how security-relevant C code is compiled, so it deserves a quick sanity check that the new wrapper preserves the same flags and symbol visibility.