feat: add arithmetic operators to Hbar

[De-real-iManuel]

Summary

Adds __add__, __sub__, and __abs__ dunder methods to the Hbar class, enabling native Python arithmetic syntax for HBAR amounts.

Changes

• Added __add__, __sub__, __abs__ to src/hiero_sdk_python/hbar.py
• All methods follow the existing comparison operator pattern (type guard, NotImplemented for non-Hbar operands)
• Added 7 unit tests to tests/unit/hbar_test.py covering basic operations, type errors, and edge cases
• All 58 tests pass, ruff linting passes

Fixes #2274

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: 27fcb84b-ce93-4248-9c2a-f31a986778cf

📥 Commits

Reviewing files that changed from the base of the PR and between eb5a870 and 696368d.

📒 Files selected for processing (1)

• tests/unit/hbar_test.py

Walkthrough

The Hbar class now supports basic arithmetic operations via three dunder methods: __add__ and __sub__ compute sums and differences of tinybar amounts, returning new Hbar instances, and __abs__ returns the absolute tinybar value. Non-Hbar operands trigger NotImplemented. Unit tests validate all cases including negative results, type errors, and zero handling.

Changes

Hbar Arithmetic Operators

Layer / File(s)	Summary
Arithmetic operators implementation src/hiero_sdk_python/hbar.py	Three dunder methods (__add__, __sub__, __abs__) enable native Python arithmetic syntax; each operates on the internal _amount_in_tinybar value and returns a new Hbar instance via Hbar.from_tinybars(), or NotImplemented for non-Hbar operands.
Arithmetic operator unit tests tests/unit/hbar_test.py	Unit tests validate Hbar addition, subtraction (including negative outcomes), absolute value, correct TypeError raising when non-Hbar operands are used with + or -, and edge cases such as Hbar.ZERO in addition.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and concisely describes the main change: adding arithmetic operators to the Hbar class.
Description check	✅ Passed	The description clearly explains the changes made, lists the methods added, mentions tests added, and references the linked issue #2274.
Linked Issues check	✅ Passed	All core objectives from #2274 are met: add, sub, abs implemented with type guards returning NotImplemented for non-Hbar operands, unit tests cover basic operations and edge cases, code style and linting verified.
Out of Scope Changes check	✅ Passed	All changes are directly related to implementing arithmetic operators for Hbar as specified in #2274; no unrelated modifications found.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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Actionable comments posted: 4

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: bb7eac1d-43bd-4b44-a6fa-9bf51abb74ec

📥 Commits

Reviewing files that changed from the base of the PR and between 7d3d212 and eb5a870.

📒 Files selected for processing (2)

• src/hiero_sdk_python/hbar.py
• tests/unit/hbar_test.py

[De-real-iManuel]

Addressed, I added isinstance checks and additional edge case tests in the follow-up commit.

[De-real-iManuel]

@ryjones

[aceppaluni]

I am not certain if the doc strings are clear here. Should we update @De-real-iManuel ?

[aceppaluni]

same here

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[manishdait]

@De-real-iManuel, thanks for the PR and the work on this!

At the moment, adding arithmetic operators to Hbar feels a bit out of scope for the SDK, mainly because the other SDKs in the Hiero ecosystem currently do not expose similar functionality. Since this could introduce cross SDK API consistency differences, I think it would be better to first discuss it in the SDK-Collaboration Hub and get feedback on it

[exploreriii]

Hi @De-real-iManuel
When you have some time, would you mind creating an issue here https://github.com/hiero-ledger/sdk-collaboration-hub/issues outlining your proposal.
This way it can be rolled out across the SDKs and we support similar services
Meanwhile as this is in discussion, I am converting this to draft