Support all output types in reverse-mode

[sritchie]

This PR:

• Adds a new mode argument to emmy.differential/extract-tangent, allowing us to use this for reverse mode instead of emmy.tape/->partials (which is now gone)
• replaces emmy.tape/extract with emmy.differential/extract-id, now part of the IPerturbed protocol.

We need these two passes because:

1. for structural outputs, we need to do a reverse-mode pass for each entry in the output. This creates a structure of Completed maps of node => sensitivity.
2. then, for each entry in a structural INPUT, we need to replace that entry with a copy of this output with that input's ID selected out

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 86.86869% with 52 lines in your changes are missing coverage. Please review.

Project coverage is 87.57%. Comparing base (f3ac544) to head (c14793b).

Files	Patch %	Lines
src/emmy/calculus/derivative.cljc	69.38%	11 Missing and 4 partials :warning:
src/emmy/collection.cljc	7.69%	5 Missing and 7 partials :warning:
src/emmy/autodiff.cljc	94.92%	5 Missing and 5 partials :warning:
src/emmy/quaternion.cljc	60.00%	4 Missing :warning:
src/emmy/dual.cljc	87.50%	2 Missing and 1 partial :warning:
src/emmy/function.cljc	93.54%	2 Missing :warning:
src/emmy/series.cljc	94.28%	2 Missing :warning:
src/emmy/tape.cljc	90.90%	1 Missing and 1 partial :warning:
src/emmy/matrix.cljc	50.00%	1 Missing :warning:
src/emmy/polynomial.cljc	50.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #169 +/- ## ========================================== - Coverage 87.68% 87.57% -0.12% ========================================== Files 99 100 +1 Lines 15792 15796 +4 Branches 850 850 ========================================== - Hits 13847 13833 -14 - Misses 1095 1113 +18 Partials 850 850 ```

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[sritchie]

Qs for @littleredcomputer:

• what do you think of this protocol approach? I am not sure there is a way around doing two passes over the output structure, annoyingly... but wdyt of the switch? Another way to do it would be to have some sort of tag type where the tag carried around info about whether it was forward or reverse mode.

Looking forward to your feedback here...

[sritchie]

Superceded by #179, #182, #183, #185