refactor(codecs): use a validated ASCII character type

[pront]

Summary

ASCII configuration fields currently use u8 with per-field Serde adapters. Configs accept a single ASCII character, but schema generation sees an integer. Introduce AsciiChar so the Rust type, serialization, and generated schema describe the same contract.

• Use the validated type for character-delimited framing and CSV delimiter, escape, and quote options. Runtime encoders and decoders still use u8.
• Replace the old adapter tests with one shared contract test covering every ASCII character, invalid inputs, defaults, round-tripping, and schema generation.
• Teach the docs generator to preserve string defaults and bump vdev to 0.3.30. Regenerated CUE files and configuration examples are unchanged.

Accepted user configurations and runtime output are unchanged. Rust callers constructing these configuration fields now use AsciiChar; byte-oriented runtime constructors are unchanged.

This is an independent prerequisite for the parse-first work, based on master, with no configuration-loader changes.

References

Related: #26475

Vector configuration

Used to compare custom framing and CSV output against the released binary:

sources:
  input:
    type: stdin
    framing:
      method: character_delimited
      character_delimited:
        delimiter: "|"
    decoding:
      codec: json
sinks:
  output:
    type: console
    inputs: [input]
    target: stdout
    encoding:
      codec: csv
      csv:
        fields: [message]
        delimiter: ","
        escape: "\\"
        quote: "$"
        double_quote: false

How did you test this PR?

• make fmt and full-workspace make check-clippy (all targets and all features).
• Scoped make test for all vector-core, codecs, and vdev tests, plus Vector HTTP/framing tests: 947 passed, no retries (2,752 outside the scope or ignored).
• Regenerated docs using the local vdev, then ran the generated-docs and component-example checks: no generated-file changes; 248 examples passed, 4 skipped.
• Built the default/vendored Vector binary on macOS arm64 and compared it with released Vector 0.58.0: five ASCII config cases matched, and the custom framing/CSV pipeline above produced byte-for-byte identical output.

Ad-hoc comparison fixtures and reports are local-only and are not included in this PR.

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

Contributor Guidelines

• Followed the Vector contributor resources and pre-push guidance.
• Future updates will preserve review history without force pushes.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-09T20:42:09.825466Z	f3d6a44	PR opened
🔒 Security Review	✅ Completed 2026-10-09T20:42:06.773260Z	f3d6a44	PR opened

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[datadoghq-integration]

More details

The shared type preserves single-ASCII-character deserialization and runtime byte conversions while making generated schemas describe string fields and retaining documentation defaults.

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