feat(encoding): add binary package

[bobzhang]

Summary

• add encoding/binary for checked fixed-width unsigned integer byte-order helpers
• add Go-compatible unsigned and signed varint encode/decode helpers with max length constants
• add generated interface metadata, README examples, and blackbox tests for round trips, views, trailing bytes, overflow, and malformed input

Scope

This intentionally covers the in-memory subset of Go-style encoding/binary. Stream-oriented read/write APIs and reflection-based struct encoding are left out because core does not have the corresponding IO abstraction in scope for this PR.

Validation

• moon check encoding/binary
• moon test encoding/binary
• moon info
• moon fmt
• moon check
• moon test

[coveralls]

Coverage Report for CI Build 4483

Coverage increased (+0.008%) to 94.097%

Details

• Coverage increased (+0.008%) from the base build.
• Patch coverage: 3 uncovered changes across 1 file (69 of 72 lines covered, 95.83%).
• No coverage regressions found.

Uncovered Changes

File	Changed	Covered	%
encoding/binary/endian.mbt	54	51	94.44%

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	15924
Covered Lines:	14984
Line Coverage:	94.1%
Coverage Strength:	206408.3 hits per line

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💛 - Coveralls

[Copilot]

Pull request overview

Adds a new encoding/binary package providing in-memory binary encoding helpers compatible with Go's encoding/binary: fixed-width unsigned integer byte-order helpers via an Endian enum, and unsigned/signed varint encode/decode functions with associated max-length constants and a Malformed error type.

Changes:

• New Endian enum with decode_uint16/32/64 and encode_uint16/32/64 methods supporting big and little endian.
• New encode_uvarint/uvarint and encode_varint/varint helpers with overflow and truncation detection.
• New package metadata, README examples, and comprehensive blackbox tests covering round trips, view offsets, overflow, and malformed input.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
encoding/binary/types.mbt	Defines Endian enum, Malformed suberror, and MAX_VARINT_LEN_* constants.
encoding/binary/endian.mbt	Implements Endian decode/encode methods using bitstring patterns for decoding.
encoding/binary/endian_test.mbt	Tests decode/encode, view offsets, round trips, and malformed inputs.
encoding/binary/varint.mbt	Implements unsigned/signed varint encode/decode with overflow checks.
encoding/binary/varint_test.mbt	Tests varint encode/decode, round trips, malformed cases, and Debug formatting.
encoding/binary/moon.pkg	Declares buffer, builtin, and debug imports, mirroring encoding/base64.
encoding/binary/pkg.generated.mbti	Generated package interface listing exported values, errors, and types.
encoding/binary/README.mbt.md	Documents byte-order and varint usage with executable mbt check examples.

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