Optimize cpptiny with single-buffer zero-copy design

[emmapowers]

Summary

• Replace dual read/write buffers with single shared buffer (~50% memory reduction)
• Add zero-copy message<T>() and send<T>() API for packed structs
• Add --unpacked flag for platforms without unaligned access support
• Add compile-time static_assert to catch platform misuse

Test plan

• C++ tests pass (34 tests)
• Arduino example builds and runs
• --unpacked mode compiles and works on ARM

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: f28daaab-4cc3-46e1-b4ce-ceb1f614358d

📥 Commits

Reviewing files that changed from the base of the PR and between 65091ba and 65938fb.

📒 Files selected for processing (10)

• bakelite/generator/cli.py
• bakelite/generator/cpptiny.py
• bakelite/generator/runtimes/cpptiny/cobs.h
• bakelite/generator/templates/cpptiny.h.j2
• bakelite/tests/generator/Makefile
• bakelite/tests/generator/test_cli.py
• docs/cpptiny.md
• examples/arduino/arduino.ino
• examples/arduino/bakelite.h
• examples/arduino/proto.h

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