Add explicit ROCS optimization modes

[fulopjoz]

What changed

• add a consistent optional optimization_mode argument to RDKit, CDPKit, and OpenEye ROCS scorers
• preserve exact legacy behavior and keys when the argument is omitted
• make explicit shape, combo, and color modes control both overlay selection and returned score
• give every explicit mode a distinct scorer key, including explicit combo
• document score ranges, compatibility, and threshold recalibration

Scientific behavior

RDKit uses opt_param values 1.0, 0.5, and 0.0 for shape, combo, and color. CDPKit color mode uses color-feature-centred starts and color ranking because CDPKit exposes no color-overlap gradient. OpenEye maps modes to internally consistent CLI flags and report columns.

Explicit RDKit combo and color can differ from legacy values because legacy DrugEx evaluated them at a shape-optimized pose. Existing tutorials remain legacy unless they opt in.

Validation

• python -m drugex.training.scorers.tests: 15 passed
• includes a flexible RDKit objective test and CDPKit end-to-end worker test
• python -m drugex.training.tests: passed
• source compilation and diff checks: passed
• licensed OpenEye CLI integration: not run

Dependency

This is a stacked fork review based on PR #6. After PR #6 is accepted, this branch should be rebased onto the updated dev branch before any upstream proposal.