docs: add Google-style docstrings to TransactionRecord

[DinethShakya23]

Description:
Add comprehensive Google-style docstrings to the TransactionRecord class to improve documentation quality, maintainability, and developer understanding.

• Add detailed module-level docstring describing the overall purpose and functionality of transaction_record.py
• Add comprehensive Google-style docstring to the TransactionRecord class, documenting all dataclass fields
• Add descriptive docstring for the __repr__(), _from_proto() explaining its conversion process from protobuf to Python objects & _to_proto() detailing serialization back to protobuf format.
• Update CHANGELOG.md

Related issue(s):
Fixes #683

Notes for reviewer:
This PR introduces documentation-only changes — no functional code or logic has been modified.

Checklist

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

[exploreriii]

Hi @DinethShakya23 approved, please rebase else let me know if I should do it for you :)

[DinethShakya23]

Hi @exploreriii ,
I have resolved the conflict. Is everything okay now?

[exploreriii]

Hi @DinethShakya23 when you merge from main you may lose the signatures if not done correctly
We recommend instead rebasing, git rebase main -S
(see rebasing.md)
Your commits are no longer verified and will be unable to merge them
Thanks

[DinethShakya23]

@exploreriii Got it. I will try to rebase my branch using git rebase main -S to keep the commits verified.
Thanks for pointing that out!

[DinethShakya23]

Hi @exploreriii ,

I think I have completed the rebase as requested. Rebased the branch onto the latest main using "git rebase -S" to ensure the commits remain GPG-signed & merge conflict in CHANGELOG.md was resolved manually & the commit (7d70486) now includes both the DCO sign-off and a valid GPG signature.

Please let me know if everything looks good from your side.

[exploreriii]

Hi, please check the workflow results and the commits tab - it tells you they are not verified
looks like you can fix this by adding your gpg key
read signing.md please 👍

[DinethShakya23]

Thanks! I have added my public key for that GPG key.

Now the commit shows as verified. Is it okay now or do I need to re-sign the commit?

[exploreriii]

Should be good! Let's wait for the final tests

[DinethShakya23]

@exploreriii
Just wanted to confirm, did I follow the correct steps to rebase? (after merging from main)

[exploreriii]

That's right, thank you very much!

[DinethShakya23]

@exploreriii Thank you! Appreciate your help and guidance!!!