fix(ttlv): parse DateTime hex values with base 16 instead of base 10

[phsym]

Summary

• Fix strconv.ParseUint base parameter in DateTime JSON decoder: 0x-prefixed values were parsed with base 10 instead of base 16, causing any value containing hex digits (a-f) to fail
• Add test case for hex-encoded DateTime decoding

[Copilot]

Pull request overview

Fixes JSON DateTime decoding for 0x-prefixed epoch values by parsing the numeric portion as hexadecimal (base 16), and adds a regression test to ensure hex-encoded DateTime values decode correctly.

Changes:

• Parse 0x-prefixed DateTime values with strconv.ParseUint(..., 16, 64) instead of base 10.
• Add a decoding test covering hex-encoded DateTime values.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
ttlv/encoding_json.go	Corrects base used when parsing 0x-prefixed DateTime values in the JSON reader.
ttlv/encoding_json_test.go	Adds a regression test validating hex DateTime decoding.

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