add section on expect vs allow

[ShahakShama]

Note

Low Risk
Low risk documentation-only change; no runtime behavior or APIs are modified.

Overview
Adds a new style.md guideline section recommending #[expect(...)] over #[allow(...)] for lint suppression, with a short rationale and example showing how #[expect] prevents stale suppressions.

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[ShahakShama]

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• allow unreachable, and expand when to use panic #13636
• add section when to return result #13635
• error types should have a Error suffix #13627
• add section on expect vs allow #13626 👈 (View in Graphite)
• delete combinators section #13416
• add section on test names #13276
• make short unit test into a recommendation #13275
• improve documentation section #13274
• remove track_caller sentence #13267
• remove sections of re-export #13266
• add logging section #13261 : 1 other dependent PR (#13262 )
• add instruction that TODOs should have an owner #13260
• add section advocating to use Self #13259
• add section on american english vs british english #13257
• remove section about private fields altogether #13166
• unite getter and setter sections, and modify setter section #13165
• reorder API sections (no text change) #13164
• add section saying that code inside macro should be formatted #13163
• add section on future returning pending #13162
• improve ai section #13147
• improve casting section #13146
• make the example in combinators compile #13145
• add comment in return value section to split checking the value and performing action to 2 lines #13144
• remove bad example in foo_or_else section #13141
• improve the starting paragraphs of testing section #13139
• improve macros section #13137
• remove unnecessary misc sections #13131
• reorder sections (move AI and Testing up) #13118
• remove open issues section #13115
• improve external dependencies section #13114
• remove github smell testing section #13113
• create misc section, move stuff into it, and order by importance (no erasure of anything yet) #13112
• change file layout section #13078
• add section on sleep in tests #13073
• add section on dependency injection #13072
• move expect message to a separate section with more explanation #13071
• add directory layout section #12950
• rename allocations and add &Option<T> #12781
• remove laziness  #11591
• rewrite types section #11588
• more comments  #11587
• more comments  #11586
• more comments  #11585
• more comments  #11584
• arithmetic: remove ditto for other mathematical operations. #11848
• gilad/style-guide

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