Prepare extension for reworked nf-lang formatter

[ewels]

Follow-up to the formatter overhaul in nextflow-io/nextflow#7346: adds the nextflow.formatting.maxLineLength setting, documents the new formatter behavior and // fmt: directives, and highlights those directives in comments.

⚠️ Do not release until nextflow-io/nextflow#7346 merges, an nf-lang release exists, and the language server ships against it.

New setting

• nextflow.formatting.maxLineLength (integer, default 120, minimum 0; 0 disables line wrapping), matching the option added to the language server. The name is a fixed contract with the language-server change.
• No client-side wiring is needed: the extension already synchronizes the entire nextflow configuration section with the language server (synchronize: { configurationSection: "nextflow" }), the same way harshilAlignment, maheshForm, and sortDeclarations work. Changes take effect without a server restart.

Documentation

• New Formatting section in the README covering the reworked formatter behavior, with wording kept consistent with docs/vscode.mdx and docs/reference/cli.mdx from the upstream PR:
  • comments are always preserved
  • K&R style (} else {) for if/else and try/catch
  • blank-line normalization
  • multi-line string re-indentation
  • automatic line wrapping at the configured maximum length
  • // fmt: skip on the last line of a statement/declaration, and // fmt: off / // fmt: on around a region
• Setting added to the README settings list, and a [Unreleased] changelog section.
• The setting description and README carry a "requires Nextflow language version 26.08 or later" note (version taken from the upstream PR docs' AddedInVersion tag — worth re-checking at release time in case the PR lands in a later release), since users can pin nextflow.languageVersion to older releases where the setting is a no-op.

Directive highlighting

• // fmt: skip|off|on comments are highlighted distinctly (scope keyword.codetag.notation.groovy, the standard codetag convention themes pick up). Implemented as a single line-comment rule with an optional capture group in the shared source.nextflow-groovy grammar, which both the script and config grammars include — so one rule covers both languages.
• The match semantics mirror the language server's directive parser exactly (//\s*fmt:\s*(skip|off|on)\s*, full-match): whitespace is flexible, but a directive followed by trailing text is not highlighted, because the formatter would ignore it. Verified against the parser source in the upstream PR branch.

Checked, no changes needed

• No extension-side tests, snippets, or docs assume Allman-style formatter output — nothing else to update.
• JSON validity and tsc --noEmit pass.

Release ordering

This PR can merge, but a release must wait for, in order:

1. Formatter overhaul: never remove comments, fmt directives, line wrapping, K&R style nextflow#7346 to merge
2. an nf-lang release containing it
3. a language server release built against that nf-lang (with matching nextflow.formatting.maxLineLength support)

Until then, existing language server releases silently ignore the new setting.

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https://claude.ai/code/session_0137gokuJdJCZDRJMsF6GbFH

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