fix: TransactionFee model rejects string gasPrice/baseFee/priorityFee from API

[jacklatourette]

Summary

The Fireblocks API returns gasPrice, baseFee, and priorityFee as strings (e.g. "1", "0.005") in the estimate_transaction_fee response. However, the TransactionFee Pydantic model declares these fields as Optional[Union[StrictFloat, StrictInt]].

StrictFloat and StrictInt reject string inputs without coercion, so Pydantic validation fails with errors like:

6 validation errors for TransactionFee
gasPrice.float
  Input should be a valid number [type=float_type, input_value='1', input_type=str]
gasPrice.int
  Input should be a valid integer [type=int_type, input_value='1', input_type=str]
baseFee.float
  Input should be a valid number [type=float_type, input_value='0.005', input_type=str]
...

The SDK then falls back to returning an UnknownBaseModel instead of EstimatedTransactionFeeResponse, which breaks downstream attribute access like response.medium.network_fee.

Fix

Add StrictStr to the union type for gas_price, base_fee, and priority_fee:

# Before
gas_price: Optional[Union[StrictFloat, StrictInt]]

# After
gas_price: Optional[Union[StrictFloat, StrictInt, StrictStr]]

This matches the actual API response format while preserving strict validation (no implicit coercion).

Reproduction

Call estimate_transaction_fee for any EVM-based asset (e.g. Base Sepolia ETH). The API returns string values for gas fields, causing the SDK to emit a UserWarning: Failed to deserialize response of type EstimatedTransactionFeeResponse and return an UnknownBaseModel.