Print coercions with context-aware parentheses

[cknitt]

The formatter currently turns foo(v :> b) into foo((v :> b)). Reuse the existing parentheses rules to omit unnecessary parentheses in calls, collections, and array indices while preserving grouping where required.

Keep parentheses for binding right-hand sides, arrow bodies, operators, field access, block sequences, constrained operands, and attributes. Bindings remain parenthesized because a following JSX element can otherwise be parsed as coercion type arguments. The parser is unchanged.

Add regression coverage for constrained operands and bindings followed by JSX, and reformat existing sources affected by the new rules.

Validation: make test, make checkformat, make test-syntax, and make test-syntax-roundtrip, plus structure-preservation and formatting-stability checks at widths 20, 80, and 100.

Fixes #6254.

[chatgpt-codex-connector]

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-04T11:30:21.476807Z	00d09b5	PR opened

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[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: 00d09b5a27

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Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

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[codecov]

Codecov Report

❌ Patch coverage is 80.43478% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.33%. Comparing base (56fe3bc) to head (df3784c).

Files with missing lines	Patch %	Lines
compiler/syntax/src/res_parens.ml	52.63%	9 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #8614   +/-   ##
=======================================
  Coverage   77.32%   77.33%           
=======================================
  Files         467      467           
  Lines       63313    63322    +9     
=======================================
+ Hits        48957    48969   +12     
+ Misses      14356    14353    -3     

Files with missing lines	Coverage Δ
compiler/syntax/src/res_printer.ml	93.07% <100.00%> (+0.12%)	⬆️
compiler/syntax/src/res_parens.ml	85.27% <52.63%> (+0.11%)	⬆️

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