fix(sdk): honor the requested encrypted-blob encoding

[s6pa1rta3n-lab]

Summary

Resolves #255 by verifying that validateEncryptedBlob in @sub-rosa/sdk strictly honors the requested encoding option ("hex" vs "base64"), rejects invalid encodings without cross-decoding fallback when an explicit encoding is requested, preserves auto-detection when omitted, and adds comprehensive unit test coverage.

Acceptance & Stipulation Checklist

• Forced hex accepts only valid hex (with and without 0x prefix).
• Forced base64 accepts only valid base64.
• Omitted encoding retains auto-detection (hex first, fallback to base64).
• Existing encrypted-blob tests, full SDK test suite, and typecheck pass without regressions.
• Reference issue Closes #255.

Changes

• Added dedicated unit tests in packages/sdk/src/encrypted-blob.test.ts verifying:
  • encoding: "hex" accepts valid hex and 0x-prefixed hex strings.
  • encoding: "hex" rejects valid base64 strings containing non-hex characters.
  • encoding: "base64" accepts valid base64 strings.
  • encoding: "base64" decodes via base64 instead of hex (verified via byte count boundary checks).
  • Omitted encoding auto-detects hex first, falling back to base64.

Closes #255

Payout Routing

• EVM (Base/Arbitrum/Polygon/ETH): 0xF46C9F6d70C50BF81ef3588AB523a90a594a2F89
• Stellar: GCL6OXAMLD75BMTINA6EMRUDWK5THQUSHMYNLSNBCJAPZJHNYJTUNIBC