[ClancyBreach]

Solana RPC transaction errors can be strings (for example, "BlockhashNotFound"), structured objects, or null. The models currently accept only objects or null, so valid string errors raise a Pydantic validation error instead of being returned to the caller.

On the current main, this reproduces the problem:

from helius.rpc.models import SignatureStatus

SignatureStatus.model_validate({
    "slot": 48,
    "confirmations": None,
    "err": "BlockhashNotFound",
    "confirmationStatus": "finalized",
})
# ValidationError: err — Input should be a valid dictionary

Extend err to str | dict | None in SignatureStatus, TransactionSignature, TransactionMetadata, and TransactionSignaturesDetail, matching the documented Solana transaction-error forms. Existing object/null values remain supported, and the field remains required.

Add 40 parametrized regression cases covering all four models and their client parsing paths, successful responses, string/object errors, invalid primitive values, and missing fields. HTTP responses are simulated with respx using synthetic fixtures based on documented RPC response shapes.

Validation on Python 3.11.9:

• Full suite: 224 passed, with network sockets disabled.
• Before the fix, the eight new string-error model/client cases failed as expected.
• basedpyright, isort, CI fatal-error flake8 checks, new-test style checks, and scoped Black checks passed.
• Full-source Black still flags the pre-existing formatting of the unchanged src/helius/laserstream/websockets.py.

No public SDK methods or dependencies are changed. No live RPC requests or blockchain transactions were used.