test: Add LiveHash unit tests

[Mounil2005]

Description:
Add comprehensive unit test coverage for LiveHash type

The LiveHash struct required additional test coverage for serialization, deserialization, and error handling paths. This PR adds five unit tests covering:

• Bytes round-trip serialization and deserialization
• Nil protobuf parameter handling with appropriate error returns
• Nil byte array parameter handling with appropriate error returns
• Protobuf conversion with nil KeyList handling
• Deprecated Duration field exclusion from serialization (only LiveHashDuration is serialized)

Related issue(s):

Fixes #1713

Notes for reviewer:
All tests pass successfully:

• TestUnitLiveHash_BytesRoundTrip (0.00s)
• TestUnitLiveHash_FromProtobufNil (0.00s)
• TestUnitLiveHash_FromBytesNil (0.00s)
• TestUnitLiveHash_ProtobufRoundTripNilKeys (0.00s)
• TestUnitLiveHash_DeprecatedDurationNotSerialised (0.00s)

The deprecated duration test confirms the invariant is properly wired in the codebase - the deprecated Duration field (time.Time) is not serialized, only LiveHashDuration (time.Duration) is used.

Checklist

• Documented (Code uses clear test names and assertions)
• Tested (All 5 unit tests pass; go build and go vet pass)

[lfdt-bot]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
see 5 files with indirect coverage changes

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[Dosik13]

Thank you for the PR! Left some suggestions

[Mounil2005]

Thanks for the suggestions @Dosik13! I've addressed all points:

• Added // SPDX-License-Identifier: Apache-2.0 after package hiero to be consistent with the other files.
• Added an Ed25519 key to the KeyList in TestUnitLiveHash_BytesRoundTrip and added an assertion to verify the key survives the round-trip.
• Replaced assert.Equal(t, errXxx, err) with require.ErrorIs(t, err, errXxx) in both nil-input tests (TestUnitLiveHash_FromProtobufNil and TestUnitLiveHash_FromBytesNil)

[Dosik13]

lgtm! Thank you for the great work!