Add sections on zero-copy and exotic types to style guide

[sffc]

Fixes #523
See #652

[coveralls]

Pull Request Test Coverage Report for Build b12ff3d821ff7e3b06e2023758668aa417d939b3-PR-699

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 231 unchanged lines in 17 files lost coverage.
• Overall coverage increased (+0.7%) to 74.188%

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Files with Coverage Reduction	New Missed Lines	%
utils/fixed_decimal/src/lib.rs	1	50.0%
utils/zerovec/src/map/kv.rs	1	64.71%
components/datetime/src/fields/length.rs	2	87.5%
components/plurals/src/error.rs	3	20.0%
components/uniset/src/lib.rs	3	11.11%
experimental/provider_ppucd/src/error.rs	3	0%
components/plurals/src/rules/parser.rs	5	96.86%
components/datetime/src/error.rs	6	9.09%
components/datetime/src/pattern/error.rs	6	25.0%
components/plurals/src/operands.rs	7	91.95%

Totals
Change from base Build 478c4a901faca10195edce477b583ed31f8fdd1f:	0.7%
Covered Lines:	8134
Relevant Lines:	10964

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💛 - Coveralls

[gregtatum]

The copy all seems reasonable to me, but I would hold off landing this until we have real examples in the code using the new ZeroCopy machinery. It seems a little early to fully require this, without any examples landed.

[nordzilla]

LGTM

[sffc]

Blocked on #652 per @gregtatum's comment above.

[codecov-commenter]

Codecov Report

Merging #699 (8972a42) into main (478c4a9) will decrease coverage by 0.19%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #699      +/-   ##
==========================================
- Coverage   74.18%   73.99%   -0.20%     
==========================================
  Files         171      182      +11     
  Lines       10802    10870      +68     
==========================================
+ Hits         8014     8043      +29     
- Misses       2788     2827      +39     

Impacted Files	Coverage Δ
components/datetime/src/error.rs	9.09% <0.00%> (-10.91%)	⬇️
components/datetime/src/pattern/error.rs	25.00% <0.00%> (-10.72%)	⬇️
components/plurals/src/rules/lexer.rs	88.17% <0.00%> (-1.94%)	⬇️
components/datetime/src/fields/symbols.rs	68.06% <0.00%> (-0.53%)	⬇️
utils/zerovec/src/map/kv.rs	64.70% <0.00%> (ø)
utils/zerovec/src/map/vecs.rs	85.10% <0.00%> (ø)
utils/fixed_decimal/src/lib.rs	50.00% <0.00%> (ø)
utils/zerovec/src/map/serde.rs	81.96% <0.00%> (ø)
components/plurals/src/operands.rs	91.95% <0.00%> (ø)
utils/zerovec/src/zerovec/serde.rs	88.05% <0.00%> (ø)
... and 118 more

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