Implement Cancel Safety using `CmdExecution` and blocks

[azriel91]

Closes #141.

Plenty to do:

• [x] CmdExecution for all *Cmds
• [ ] API refinement
• [x] Use interruptible between CmdBlock executions.

All very large tasks.

Don't forget:

• [x] Replace panic!s in fetches with Error (probably).
• [x] Include the CmdBlock::Input and Outcome types in the error message.
• [x] Include the CmdExecution's chain of CmdBlocks in the error message.
• [ ] Pass in state_clean from the StatesClean map, instead of allocating another.
• [x] Use interruptible in each CmdBlock's item iterator.

[codecov[bot]]

Codecov Report

Attention: 220 lines in your changes are missing coverage. Please review.

Comparison is base (1f3561d) 92.45% compared to head (38afe59) 93.42%.

Files	Patch %	Lines
...src/cmd_blocks/apply_state_sync_check_cmd_block.rs	79.94%	71 Missing :warning:
crate/rt/src/cmd_blocks/apply_exec_cmd_block.rs	91.16%	31 Missing :warning:
crate/cmd_rt/src/cmd_execution.rs	90.14%	28 Missing :warning:
...ate/rt/src/cmd_blocks/states_discover_cmd_block.rs	96.67%	18 Missing :warning:
crate/cmd_rt/src/cmd_block/cmd_block_wrapper.rs	82.85%	12 Missing :warning:
...t/src/cmd_execution/cmd_execution_error_builder.rs	93.38%	8 Missing :warning:
crate/cmd/src/scopes/single_profile_no_flow.rs	22.22%	7 Missing :warning:
crate/rt/src/cmd_blocks/diff_cmd_block.rs	94.28%	6 Missing :warning:
crate/cmd/src/scopes/single_profile_single_flow.rs	66.66%	5 Missing :warning:
crate/rt/src/cmds/ensure_cmd.rs	96.75%	5 Missing :warning:
... and 15 more

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #163 +/- ## ========================================== + Coverage 92.45% 93.42% +0.97% ========================================== Files 378 404 +26 Lines 35781 40999 +5218 ========================================== + Hits 33080 38305 +5225 + Misses 2701 2694 -7 ```

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