Add params schema support to ProcessNode and align legacy _from_scriptconfig

[Erotemic]

Motivation

• Allow ProcessNode subclasses to declare a scriptconfig-style schema via a params class variable so path/parameter groups can be derived without factory helpers.
• Preserve backwards compatibility by keeping the EXPERIMENTAL _from_scriptconfig helper while making it follow the same derivation rules as the new params mechanism.
• Make grouping/tag rules explicit (in/out/algo/perf/primary) and handle defaults/warnings consistently when deriving groups from a schema.

Description

• Introduce an optional class variable params on ProcessNode and merge derived groups into instance in_paths, out_paths, algo_params, perf_params, and primary_out_key during __init__ only where values are missing so explicit ctor/classvars take precedence.
• Add a shared helper ProcessNode._derive_groups_from_params_spec(params_spec) that accepts a scriptconfig.DataConfig class or instance, or a plain dict, and returns (in_paths_set, out_paths_dict, algo_params_dict, perf_params_dict, primary_out_key) while implementing the following rules: no tags => algo param, raise ValueError on conflicting bucket tags, ignore (with warnings.warn) defaults for in_paths, use non-empty string defaults for out_paths, and include instance-provided defaults when params is an instance.
• Update the legacy @classmethod _from_scriptconfig to call the shared helper and construct a ProcessNode using the same derivation rules while keeping it marked EXPERIMENTAL and treating it as a compatibility helper.
• Add doctest-style examples demonstrating: untagged param becomes an algo default, in_path default triggers a warning and is ignored, explicit out_paths on the node override schema defaults, and parity between params-based derivation and _from_scriptconfig.
• Minor plumbing: import warnings, ensure safe merging when in_paths/out_paths/algo_params/perf_params may be None, and preserve existing behavior of self.config and configure().

Testing

• No automated tests were executed as part of this change (doctest examples were added to pipeline.py but not run).

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Codex Task