Use Nextflow's plain values of Channel and Value params

[pinin4fjords]

Important

Waiting for a Nextflow release. The Nextflow side (nextflow-io/nextflow#7759, closing nextflow-io/nextflow#7758) is merged, but not in a release yet. This PR sets nextflowVersion = '26.10.0', so it won't build until Nextflow 26.10.0 is out. After that, merging master in (and adjusting the version if the release number differs) should be all it needs.

@nvnieuwk, for your awareness: this is the follow-up to the TODO from #230.

What it does

Nextflow now gives the value each typed Channel and Value param was created from through session.params.toPlainMap(). This PR uses that in validateParameters() and the params summary, and removes nf-schema's own lookup in the config (replaceDataflowParams and its helpers in Common.groovy). Typed params now reach the schema in their declared types and with their script defaults, which the config lookup could not give.

The dataflow tests from #230 are rewritten to use real typed params blocks, and the mocked-session spec (ValidateDataflowParamsTest) is replaced by them.

Open questions

• Minimum Nextflow version. This raises nf-schema's requirement from 26.04.0 to 26.10.0. Is that OK, or should nf-schema keep supporting older Nextflow? If so, the call could check that toPlainMap() exists and fall back to session.params (no older Nextflow release has typed Channel/Value params).
• Legacy channel params. A channel assigned to params in the script (params.x = channel.of(...), not declared in a params block) was handled by Validate and print the value of Channel and Value params instead of hanging #230's config lookup but isn't covered by toPlainMap(). Is it fine to drop that case?
• Changelog. I've put the entry under a new 3.2.0, assuming 3.1.0 goes out before Nextflow 26.10.0. Does that match your plans?

Testing

All 161 tests pass against a local build of Nextflow master (3e6b01d35, which includes nextflow-io/nextflow#7759) published as 26.10.0. With session.params in place of session.params.toPlainMap(), the new tests fail, several by hitting their timeout.

🤖 Generated with Claude Code

[nvnieuwk]

Thanks already! We can come back to this after the release next week 🎉