Fix potential crashes and unhandled exceptions in spark-character loaders

[Ra229287]

Packet

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    "id": "vibeforge1111/spark-character",
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  "issue": {
    "type": "bug",
    "severity": "medium",
    "title": "Potential unhandled crashes in spark_character loaders",
    "actual_behavior": "Various character loader functions raise raw tracebacks on invalid inputs.",
    "expected_behavior": "Should gracefully return defaults.",
    "repro_steps": [
      "Pass invalid types to _require_mapping",
      "Pass invalid types to _validate_score",
      "Pass invalid types to validate_chip_yaml_spec",
      "Pass invalid types to _coerce_lab_chip",
      "Pass invalid types to _coerce_yaml_dict"
    ],
    "affected_workflow": "Character loading"
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