Add Starknet On-ramp Support on Noblocks

[SarahSync]

Description
Off-ramp is supported on Starknet on Noblocks today. This feature adds on-ramp support on Starknet so that users can on-ramp into stablecoins on Starknet on Noblocks in the same way they can on the other supported networks where on-ramp is available.

User Story
As a Noblocks user,
I want to on-ramp into stablecoins on Starknet,
So that I can fund a Starknet wallet on Noblocks just like I can on the other supported networks.

Acceptance Criteria

1. GIVEN a user opens the on-ramp flow on Noblocks
   WHEN they view the list of supported networks for on-ramp
   THEN Starknet is displayed alongside the other supported on-ramp networks.

2. GIVEN a user selects Starknet on the on-ramp flow
   WHEN the selection is made
   THEN the on-ramp flow updates to reflect Starknet as the selected network, including the supported tokens and any Starknet-specific input fields.

3. GIVEN Starknet is the selected network on the on-ramp flow
   WHEN the user enters an amount and views the conversion
   THEN the conversion rate between the selected fiat currency and the Starknet token is displayed correctly.

4. GIVEN Starknet is the selected network on the on-ramp flow
   WHEN the user proceeds through the on-ramp flow (recipient/payment details, review, payment, confirmation)
   THEN each step works on Starknet in the same way as on other supported on-ramp networks.

5. GIVEN a user completes a Starknet on-ramp transaction
   WHEN they view the transaction confirmation
   THEN the transaction details (amount, token, network, on-chain reference, explorer link) reflect Starknet correctly and the funds arrive at the user's Starknet wallet.

Tech Details

• Add Starknet to the list of supported networks for on-ramp.
• Add support for Starknet-compatible tokens used on Noblocks (e.g., USDC, USDT on Starknet).
• Ensure rate fetching, conversion logic, and supported fiat corridors work for Starknet on-ramp.
• Ensure on-ramp creation, processing, and confirmation flows work end-to-end on Starknet.
• Link transaction confirmations to the appropriate Starknet block explorer.

Notes/Assumptions

• Off-ramp on Starknet is already supported on Noblocks; this ticket extends the same network to on-ramp.

Open Questions

• Will Starknet on-ramp follow the same user-facing flows as on-ramp on other supported networks?.
• Which tokens on Starknet will be supported for on-ramp at launch?
• Which fiat corridors will be supported for Starknet on-ramp at launch?
• Are there Starknet-specific wallet or address requirements that the on-ramp flow must handle?