Roadmap to support AVR/8-bit chipset

(Summarizing the discussions at https://github.com/intel/compile-time-init-build/discussions/105 ... Please feel free to revise the roadmap below.)

1. [ ] Wait for ISO C++26 standard to publish, which requires the standard library `` to be part of the freestanding C++ toolchain;
2. [ ] Work with team behind the project [avr-libstdcpp](https://github.com/modm-io/avr-libstdcpp) to include a subset of `` features. https://github.com/modm-io/avr-libstdcpp?tab=readme-ov-file#notable-adaptions-and-limitations
3. [ ] If step 2 is blocked, convince the fmtlib team to remove the line `#include ` in the header-only library, or make it an optional `#include` similar to how `#include ` is made optional.
4. [x] If step 2 and 3 are blocked, convince the `compile-time-init` team to make `#include ` optional.
5. [ ] If step 2, 3, and 4 are all "no go", the feature is clearly stuck in a multi-team, multi-project stalemate. maybe we should give up on Microchip/Atmel AVR chipset support in the `compile-time-init` framework. (After all, the limited 16-bit address space, and the Harvard architecture may not justify `cib`'s complexity.)
6. [X] Or, use an outdated version without the latest features, e.g. RLE encoding of the command router, i.e. right before #338 .