Redesign Config schema and validation to align with ProbeSpec/ScanSpec style

[coderabbitai]

Overview

The current Config schema and validation layer (in zea/internal/config/validation.py) is planned for a full redesign in a future PR to align it with the ProbeSpec/ScanSpec pattern already used elsewhere in the codebase.

Motivation

• The current schema-library-based validation approach is inconsistent with the Spec-based validation used for ProbeSpec and ScanSpec.
• The parameters section of the config should accept any parameter key, reflecting the same open/extensible design of the zea.Parameters class (which supports arbitrary custom pass-through parameters via _custom_params).
• Until the redesign, ignore_extra_keys=True is used as a pragmatic workaround at both the parameters schema level and the top-level config_schema.

Planned changes

• Remove the current schema/validation infrastructure for Config.
• Redesign validation in line with ProbeSpec/ScanSpec (i.e., dataclass-based Spec subclasses).
• Ensure the parameters group allows arbitrary keys, consistent with zea.Parameters.

References

• PR Parameters redesign #392 (parameters redesign): Parameters redesign #392
• Originating review comment: Parameters redesign #392 (comment)

/cc @tristan-deep