Beautify and fix the API documentation

*   Fix INT -> SAFE_INT

*   Remove completed TODOs

*   Clarify example titles

*   Fix missing rtvref.validation and rtvref.validator docs

    Also rename `validation/isValidator -> validation/isCustomValidator`
    to avoid confusion between custom validators in typesets, and
    type validators in the library.

*   Clarify rtv.t and rtv.q enumerations

*   Clean-up the rtv interface
7 jobs for master in 16 minutes and 23 seconds
Status Job ID Name Coverage
  Build
passed #100542392
build

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  Test
passed #100542398
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code_quality

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container_scanning

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dependency_scanning

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license_management

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sast

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test

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