feat(encoding): add hex package

[bobzhang]

Summary

• add moonbitlang/core/encoding/hex for in-memory lowercase hexadecimal encoding and decoding
• add Go-style encoded_len / decoded_len helpers
• document malformed input behavior and include README examples

Scope

• intentionally excludes stream encoder/decoder APIs because core does not expose an IO abstraction here
• keeps the first PR focused on deterministic in-memory operations

Validation

• moon check
• moon test encoding/hex
• moon test

[Copilot]

Pull request overview

Adds a new moonbitlang/core/encoding/hex package providing deterministic, in-memory lowercase hexadecimal encoding/decoding utilities, mirroring Go’s encoding/hex API style (including encoded_len/decoded_len) and documenting malformed-input behavior.

Changes:

• Introduces encode, decode, encoded_len, and decoded_len APIs plus a Malformed error type.
• Adds comprehensive unit tests for encoding/decoding (including all-byte roundtrip and malformed inputs).
• Adds package README with runnable examples.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
encoding/hex/README.mbt.md	Documents API, malformed behavior, and provides runnable examples.
encoding/hex/pkg.generated.mbti	Generated public interface for the new package.
encoding/hex/moon.pkg	Declares package imports needed by the implementation/tests.
encoding/hex/encode.mbt	Implements lowercase hex encoding and encoded_len.
encoding/hex/encode_test.mbt	Tests encoding correctness and encoded_len.
encoding/hex/decode.mbt	Implements hex decoding, decoded_len, and Malformed error.
encoding/hex/decode_test.mbt	Tests decoding correctness, malformed handling, and Debug output.

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[coveralls]

Coverage Report for CI Build 4482

Coverage increased (+0.008%) to 94.097%

Details

• Coverage increased (+0.008%) from the base build.
• Patch coverage: 21 of 21 lines across 2 files are fully covered (100%).
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	15873
Covered Lines:	14936
Line Coverage:	94.1%
Coverage Strength:	207071.71 hits per line

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💛 - Coveralls