refactor: add structured validation metadata and fix contract client …

[whitezaddy]

…test workspace instability
Closes #129

🚀 #Refactor: Structured Metadata Validation Exceptions

Overview

This Pull Request transitions the input validation pipeline from throwing unstructured, string-based exceptions to throwing strongly-typed, machine-readable GuildPassError metadata blocks. This enables consumers to isolate exactly which configuration field or entity parameter failed and why without fragile string parsing.

Key Changes

• Validation Standardization: Implemented a unified throwValidationError helper inside src/utils/validation.ts ensuring consistent output object shape mapping (field, reason, value, valueType).
• Masking Invariants: Added strict string checking to mask and sanitize sensitive pipeline keys (e.g., apiKey) from leaking through exception details blocks.
• Workspace Stability Fixes: Corrected long-standing missing scope imports (DECIMALS_SELECTOR and formatUnits) and added strict regex digit/decimal boundaries inside src/contracts/contractClient.ts.

Verification Checklist

• All 375 unit and integration tests executing cleanly inside Vitest framework.
• Sensitive parameters scrubbed from error details context.
• Form fields properly categorized with REQUIRED, INVALID_FORMAT, and INVALID_TYPE metadata keys.