CSV parsing allows duplicate crypto tokens.

[bbresearcher]

Describe the bug
The CSV parsing function and code allows for the CSD import to contain duplicate crypto tokens.
This was discussed and does not seem to have any security impact however it was decided to restrict columns to be unique.

To Reproduce
using any csv data as below still works.

username,balance_ETH_ETH,balance_ETH_ETH
dxGaEAii,11888,41163
MBlfbBGI,67823,18651

running the command cargo run --release --example summa_solvency_flow still generates successfully.

1. Ownership proofs are submitted successfully!
2. Commitment is submitted successfully!
3. Exported proof to user #1, as `user_1_proof.json`
4. Verifying the proof on contract veirifer for User #1: true

Expected behavior
Crypto token columns should be unique