feat(Singlepass, Cranelift): add --enable-unaligned-memory-accesses (v2)

[marxin]

Right now, the RISC-V single-pass compiler emits 1-byte loads and stores (as a runtime check) to avoid strict alignment violations. This PR changes the default to use full-size native load/store operations, while still providing an option to retain the previous behavior. Similarly, for Cranelift, we now support this functionality by incorporating @wakabat’s changes.

@tsahee @wakabat - can you test the change if it fits your needs?

Relates: #6024

[Copilot]

Pull request overview

This PR introduces an opt-in --enable-unaligned-memory-accesses switch to control whether the Cranelift and Singlepass (RISC-V) compilers emit runtime-safe handling for potentially unaligned memory loads/stores, alongside adding a WAST regression test for unaligned accesses.

Changes:

• Add CLI flag --enable-unaligned-memory-accesses and plumb it into Cranelift and Singlepass compiler configurations.
• Implement Cranelift-side unaligned load/store handling via aligned fast-path + bytewise slow-path.
• Add a WAST test plus test-harness wiring to exercise unaligned loads/stores when the flag is enabled.

Reviewed changes

Copilot reviewed 13 out of 14 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/wast/wasmer/unaligned-memory-access.wast	Adds a WAST test exercising unaligned load/store behaviors.
tests/compilers/wast.rs	Enables unaligned-handling in test runs for the new unaligned WAST.
tests/compilers/config.rs	Plumbs an allow_unaligned_memory_accesses test config option into compiler setup.
lib/compiler/src/compiler.rs	Adds a CompilerConfig hook method for enabling unaligned access handling.
lib/compiler-singlepass/src/machine.rs	Updates RISC-V MachineRiscv::new call sites to pass the new flag argument.
lib/compiler-singlepass/src/machine_riscv.rs	Stores and uses the unaligned-access flag to select safe vs native load/store sequences.
lib/compiler-singlepass/src/config.rs	Exposes allow_unaligned_memory_accesses configuration on Singlepass.
lib/compiler-singlepass/src/compiler.rs	Wires Singlepass config flag into MachineRiscv::new.
lib/compiler-cranelift/src/translator/func_translator.rs	Threads the unaligned-access flag through function translation.
lib/compiler-cranelift/src/translator/code_translator.rs	Implements runtime alignment check + bytewise slow-path for loads/stores when enabled.
lib/compiler-cranelift/src/config.rs	Adds config storage and CompilerConfig enable hook for unaligned access handling.
lib/compiler-cranelift/src/compiler.rs	Passes the flag into FuncTranslator creation (both non-rayon and rayon paths).
lib/cli/src/backend.rs	Adds the --enable-unaligned-memory-accesses flag and applies it to Cranelift/Singlepass configs.
.gitignore	Adds .codex to ignored files.