feat: Allow PublicKey for TokenCreateTransaction keys

[Adityarya11]

Description

This PR enhances TokenCreateTransaction to accept both PublicKey and PrivateKey objects for all token key fields (admin, supply, freeze, wipe, etc.), enabling non-custodial transaction construction.

With this change, an application (e.g., an automated agent) can build a transaction using only a user’s PublicKey, serialize it to bytes, and then return it for the user to sign locally with their PrivateKey — preserving ownership and key isolation.

This implementation follows the pattern used in the TypeScript SDK and aligns with TopicCreateTransaction.py behavior, as previously suggested by the maintainer.

---

Key Changes

• Introduced Key = Union[PrivateKey, PublicKey] type alias for flexibility and backward compatibility.

• Updated the TokenKeys dataclass and all set_*_key() methods to accept the new Key type.

• Re-implemented _to_proto_key() to:

  • Serialize only public key bytes;
  • Automatically derive the public key from a PrivateKey via .public_key();
  • Raise TypeError for unsupported key types.

• Added comprehensive unit and integration tests to ensure safety and parity:

  • Validates both ED25519 and ECDSA key types.
  • Ensures only public-key data is serialized in the proto.
  • Verifies private-key bytes are never embedded in serialized transaction bytes.

---

Security & Safety

• Distinguishes between PrivateKey and PublicKey by Python class type, not by raw bytes — avoiding ambiguity where ED25519 key bytes might appear identical.
• Guarantees private material is never serialized or exposed in protobuf representations.
• Added negative tests confirming serialized transactions contain only public-key fields.

---

Compatibility

• Fully backward compatible — existing code using PrivateKey continues to work.
• New usage allows explicit passing of PublicKey for non-custodial scenarios.

Example:

tx = (
    TokenCreateTransaction()
    .set_token_name("MyToken")
    .set_token_symbol("MTK")
    .set_supply_key(user_public_key)
    .freeze()
    .to_bytes()
)
# Agent sends tx bytes to user for signing with their PrivateKey

---

Parity with TypeScript SDK

Behavior now matches the JS SDK:

• Accepts either key type (PrivateKey or PublicKey)
• Always serializes the public representation internally
• Enables agents to construct unsigned, serializable transactions securely

---

Related Issue

Fixes #735

---

Checklist

• Backward compatible (no breaking changes)
• Aligned with JS SDK behavior
• Unit and integration tests added (ED25519, ECDSA, and non-custodial flow)
• Security verified (no private-key bytes in serialized proto)
• Documented in CHANGELOG.md

[exploreriii]

Hi @Adityarya11
Good efforts with this, and lots of good content
Some of the tests are using unusual methods that sometimes don't test what you are intending -- this is normal, being fairly new to the sdk, but building knowledge will help improve your accuracy over time
I'd recommend checking with us @nadineloepfe @exploreriii @manishdait and see who may be available over the next few days

[Adityarya11]

Hi @Adityarya11 Good efforts with this, and lots of good content Some of the tests are using unusual methods that sometimes don't test what you are intending -- this is normal, being fairly new to the sdk, but building knowledge will help improve your accuracy over time I'd recommend checking with us @nadineloepfe @exploreriii @manishdait and see who may be available over the next few days

Sorry for lots of confusion in my comments and imports, i am refactoring my code again and will fix ASAP.
thanks

[Adityarya11]

@exploreriii can you please approve the test workflow so that i can check whether tests are failing or not...
thanks

[Adityarya11]

@manishdait fixing all the issues ASAP
Thanks.

[Adityarya11]

Hello @exploreriii,
Could you please approve the test workflow run for this PR?... I'd like to check the test results.

Additionally, when either you or @manishdait have a moment, I would appreciate a review.

Thanks

[exploreriii]

Yes, thank you for the reminder @Adityarya11
I will try and study the issue and get back to you in the next day or so

[exploreriii]

Hi @Adityarya11
Well done - thank you for taking the time to get the details
I think this is great
I will pass on to @nadineloepfe or @manishdait for a second opinion as keys are sensitive

[exploreriii]

also, please rebase and change this line

• feat: Allow PrivateKey to be used for keys in TopicCreateTransaction for consistency.
• in your changelog

to the new unreleased section as we have released 0.1.8 now

[exploreriii]

Requesting second opinion @nadineloepfe or @manishdait for as keys are sensitive