feat: enforce Tanzania mobile number format validation with Tigo/Vodacom prefix checking

[zeroknowledge0x]

Fixes #1039

Summary

Implements Tanzania-specific mobile phone number validation with operator prefix checking for all major Tanzanian mobile network operators.

Changes

• New Tanzania provider prefix mappings for 5 operators:
  • Vodacom: +25575, +25576, +25577, +25578
  • Tigo (Mixx by Yas): +25565, +25567, +25571
  • Airtel Tanzania: +25568, +25569
  • Halotel: +25562, +25563
  • TTCL: +25573
• **** — validates E.164 format (+255XXXXXXXXX) and local format (0XXXXXXXXX), identifies operator
• **** — validates phone number belongs to the expected provider's prefix band
• Transaction controller integration — Tanzania numbers automatically route to Tanzania-specific validation
• Comprehensive tests — 20+ test cases covering all operators, local format, and error scenarios

Testing

• ✅ All Vodacom prefixes (075, 076, 077, 078) validated correctly
• ✅ All Tigo prefixes (065, 067, 071) validated correctly
• ✅ Airtel Tanzania prefixes (068, 069) validated correctly
• ✅ Local format (0XXXXXXXXX) auto-normalized to E.164
• ✅ Invalid prefixes rejected with descriptive error messages
• ✅ Wrong-length numbers rejected with format guidance
• ✅ Non-numeric characters rejected

Technical Details

• Country code: +255
• Number format: +255 + 9 digits (12 total) or 0 + 9 digits (10 total local)
• Prefix validation ensures numbers belong to active Tanzania MNO allocations
• Backward compatible — existing validation for other regions unchanged

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