Implement Cancel Safety using CmdExecution and blocks

[azriel91]

Closes #141.

Plenty to do:

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

All very large tasks.

Don't forget:

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

[codecov]

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

Additional details and impacted files

@@            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     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.