Simplify the CPI messaging.

[eirrgang]

• RP TaskDescription metadata field changes from a dict to a `tuple[str, None|dict]`` of operation name and operand.
• scalems.messages.Command class hierarchy is replaced by simple TypedDicts and utility functions in new scalems.cpi module.
• CpiCommand._command_name() replaces CpiCommand.command_class() required classmethod to support scalems.radical.CpiCommand subclass registration (for creation function dispatching).
• Update signature for scalems.radical.manager.RuntimeManager.cpi().

Ref #377

[codecov[bot]]

Codecov Report

Patch coverage: 86.95% and project coverage change: -0.15% :warning:

Comparison is base (b162150) 78.65% compared to head (1e0a1e4) 78.50%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #387 +/- ## ========================================== - Coverage 78.65% 78.50% -0.15% ========================================== Files 33 34 +1 Lines 4090 4062 -28 Branches 643 638 -5 ========================================== - Hits 3217 3189 -28 + Misses 630 629 -1 - Partials 243 244 +1 ``` | [Files Changed](https://app.codecov.io/gh/SCALE-MS/scale-ms/pull/387?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=SCALE-MS) | Coverage Δ | | |---|---|---| | [src/scalems/radical/manager.py](https://app.codecov.io/gh/SCALE-MS/scale-ms/pull/387?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=SCALE-MS#diff-c3JjL3NjYWxlbXMvcmFkaWNhbC9tYW5hZ2VyLnB5) | `73.46% <80.00%> (-0.52%)` | :arrow_down: | | [src/scalems/cpi.py](https://app.codecov.io/gh/SCALE-MS/scale-ms/pull/387?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=SCALE-MS#diff-c3JjL3NjYWxlbXMvY3BpLnB5) | `85.29% <85.29%> (ø)` | | | [src/scalems/radical/raptor/\_\_init\_\_.py](https://app.codecov.io/gh/SCALE-MS/scale-ms/pull/387?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=SCALE-MS#diff-c3JjL3NjYWxlbXMvcmFkaWNhbC9yYXB0b3IvX19pbml0X18ucHk=) | `83.67% <91.30%> (+0.20%)` | :arrow_up: | | [src/scalems/messages.py](https://app.codecov.io/gh/SCALE-MS/scale-ms/pull/387?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=SCALE-MS#diff-c3JjL3NjYWxlbXMvbWVzc2FnZXMucHk=) | `73.07% <100.00%> (-14.43%)` | :arrow_down: | | [src/scalems/radical/executor.py](https://app.codecov.io/gh/SCALE-MS/scale-ms/pull/387?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=SCALE-MS#diff-c3JjL3NjYWxlbXMvcmFkaWNhbC9leGVjdXRvci5weQ==) | `65.94% <100.00%> (ø)` | | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/SCALE-MS/scale-ms/pull/387/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=SCALE-MS)

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