Prepare extension for reworked nf-lang formatter

[ewels]

Prepares the extension for the reworked nf-lang formatter. The formatter overhaul (nextflow-io/nextflow#7346) merged scoped down to comment preservation; the extension-facing features now live in stacked follow-ups — line wrapping in nextflow-io/nextflow#7520 and fmt: directives in nextflow-io/nextflow#7522. This PR adds the nextflow.formatting.maxLineLength setting, documents the new formatter behavior, and highlights fmt: directives in comments.

⚠️ Do not release until nextflow-io/nextflow#7520 and nextflow-io/nextflow#7522 merge, an nf-lang release contains them, and the language server ships against it.

Upstream status

The original formatter overhaul PR (nextflow-io/nextflow#7346) merged containing comment preservation and multi-line string re-indentation only. The remaining features were split into stacked PRs: include sorting (#7519) ← line wrapping (#7520) ← fmt: directives (#7522), plus blank-line normalization (#7523). K&R-style else/catch was dropped. This PR's docs and features have been aligned to that split.

New setting

• nextflow.formatting.maxLineLength (integer, default 120, minimum 0; 0 disables line wrapping), matching the -line-length option from Wrap long lines in the formatter nextflow#7520 and the corresponding language-server setting. 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, with wording aligned to the upstream docs:
  • comments are always preserved (merged in #7346)
  • multi-line string re-indentation (merged in #7346)
  • automatic line wrapping at the configured maximum length (#7520)
  • // fmt: skip on the last line of a statement/declaration, and // fmt: off / // fmt: on around a region (#7522)
• Setting added to the README settings list, and a [Unreleased] changelog section linking the upstream PRs.
• The setting description and README note that line wrapping and the directives are ignored by older language server versions (deliberately version-agnostic, since the follow-up PRs are unmerged — pin the exact version at release time). 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 directive parser in Support fmt: skip / off / on directives in the formatter nextflow#7522 exactly (FmtDirectives.FMT_DIRECTIVE = //\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. Re-verified against the formatter-fmt-directives branch after the split — the regex is unchanged.

Checked, no changes needed

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

Release ordering

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

1. Wrap long lines in the formatter nextflow#7520 (line wrapping) and Support fmt: skip / off / on directives in the formatter nextflow#7522 (fmt: directives) to merge — #7520 is stacked on #7519, and #7522 on #7520
2. an nf-lang release containing them
3. a language server release built against that nf-lang (with matching nextflow.formatting.maxLineLength support)

At release time, update the version notes in the README and setting description with the actual required language server version. Until then, existing language server releases silently ignore the new setting.

🤖 Generated with Claude Code

https://claude.ai/code/session_0137gokuJdJCZDRJMsF6GbFH