feat: support hbar transfer

[prajeeta15]

Add Hbar object support to TransferTransaction and add tests

Allow _add_hbar_transfer, add_hbar_transfer, and add_approved_hbar_transfer to accept Hbar objects in addition to raw integer tinybar amounts. Normalize Hbar inputs to tinybars immediately (via Hbar.to_tinybars()), store the resulting tinybar integer in HbarTransfer, and keep existing integer behavior intact. Add comprehensive unit tests covering the new behavior and edge cases.

• Accept Union[int, Hbar] for _add_hbar_transfer, add_hbar_transfer, and add_approved_hbar_transfer.
• Add runtime type validation and raise TypeError for invalid account_id, amount, or is_approved types.
• Normalize Hbar to tinybars via Hbar.to_tinybars() and store the tinybar integer in HbarTransfer.
• Reject zero-value transfers (ValueError for zero tinybar amounts).
• Accumulate multiple transfers to the same account_id by adding tinybars.
• Add unit tests (tests/unit/transaction/test_transfer_transaction.py) that cover:
  • constructor behavior with pre-populated transfers,
  • adding HBAR transfers with integer tinybars,
  • adding HBAR transfers with Hbar objects (HBAR and TINYBAR units),
  • approved HBAR transfers with Hbar objects,
  • accumulation for mixed Hbar and int inputs,
  • zero-value validation for ints and Hbar(0),
  • invalid-type validation for amount,
  • conversion accuracy from various Hbar units to tinybars,
  • existing token and NFT transfer behavior, building transaction and scheduled bodies, and frozen transaction behavior.
• Update changelog with an Added entry describing the feature and tests.

Related issue(s):

Fixes #917

Notes for reviewer:

• Backwards compatible: integer inputs behave exactly as before.
• Hbar inputs are normalized immediately to tinybars; the Hbar object is not stored—only the tinybar integer is stored in HbarTransfer.
• Type validation:
  • account_id must be an AccountId instance (TypeError otherwise).
  • amount must be an int or Hbar (TypeError otherwise).
  • is_approved must be bool (TypeError otherwise).
• Zero amounts are rejected with ValueError("Amount must be a non-zero value.").
• Tests added exercise both positive and negative amounts, edge large/small integer boundaries, token/NFT behavior, and frozen transaction immutability.
• Suggested reviewers should pay attention to any consumers of HbarTransfer (ensure they expect tinybar integers) and to Hbar.to_tinybars() behavior.

Checklist

• Documented (Code comments, README, changelog entry)
• Tested (unit, integration, etc.)

[exploreriii]

@tech0priyanshu if you are available for a review

[exploreriii]

Hi @prajeeta15 this branch I think was a branch from your workflow check? or a non-updated main?
You are submitting https://github.com/hiero-ledger/hiero-sdk-python/pull/942/files
two PRs: one for PR check and one for hbar

Please make sure to pull latest changes to main, ensure your origin is matching the upstream main, and then rebase your branch with that -- you may want to make a new branch

[prajeeta15]

i switched branches (just before push) to push the latest changes so I think the last PR commit (from old branch) got here too (git push oldbranch: new branch) .. but that was already merged and I had taken latest upstream from main.
the old PR was already merged so I don't think it would create a problem ? idk

[exploreriii]

Over the weekend we had to apply a hot fix, and pulled split the workflow in two
Recommendation always pull from main, else, can check the diff from main before publishing

[exploreriii]

You changed the error return to:
raise ValueError("Amount must be a non-zero value.")
Please add a Breaking Change section
and briefly document that small breaking change

aditinally, make sure your tests are changed to grab this new error message

[exploreriii]

This conversion is incorrcet

[exploreriii]

maybe also edit
tests/integration/transfer_transaction_e2e_test.py
to test hbar units?

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