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.)

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[exploreriii]

Requet review if available @MonaaEid @Adityarya11

[exploreriii]

Hi @prajeeta15 please rebase and also add your changelog check correctly :)
thank you

[Adityarya11]

Hi @prajeeta15 please rebase and also add your changelog check correctly :) thank you

hi @prajeeta15 if the ChangeLog is messed up you may try git checkout main -- CHANGELOG.md
then add your change then push force
but first rebase and fetch the upstream
Thanks

[exploreriii]

yes agree, you can just copy in the main's changelog code then add your change on top and commit that.

[prajeeta15]

updated changelog

[Adityarya11]

updated changelog

Hi @prajeeta15
Change log should only contain your feature
Only one addition in file
You can do
Git checkout main -- CHANGELOG.md
The. Just add one line of your work , commit and push the commit
Thanks

[prajeeta15]

@Adityarya11 yeah I was having an issue during rebase so I had just copy-pasted the current changelog.md from main to this. but cool. i pulled and updated changelog with just my lines of work.

[exploreriii]

Request review if available @hiero-ledger/hiero-sdk-python-triage

[AntonioCeppellini]

what could happen if the amount is equal to 0 here?

[AntonioCeppellini]

I'd keep the previous version, is a bit cleaner and also here you have two if with quite te same condition:

1. if not isinstance(amount, int) or amount == 0 (look after the or)
2. if amount == 0