Add reusable pre-transmission validation

[tiagoapolo]

What changed

• makes validateDpsJsonRequest the canonical non-throwing API returning structured reports
• changes DpsFiscalValidationError to carry structured issues and its complete report
• expands structural, fiscal, date, value, address, and environment validation
• adds DPS XML validation against the official v1.01 XSD
• adds certificate validity and holder checks
• splits preparation/signature verification from network transmission
• packages the official XSD files and bumps the SDK to 2.0.0 for the breaking contract

Why

API and worker need one source of truth for DPS structure and final technical validation so known-invalid payloads never reach SEFIN.

Impact

Consumers can call validateDpsJsonRequest, persist a normalized validation report, prepare a signed DPS, and transmit it only after persistence. Builders use assertValidDpsJsonRequest when invalid input must throw. Runtime preparation requires xmllint.

Validation

• npm test — 38 tests passed
• npm run build
• npm pack --dry-run verified that XSD files are included