Bug Report: Unexpected Asset Allocation Merge After Sending Another Asset

[astral-bitlight]

Description
When sending assets of one type (Asset 2), the UTXO allocations of another unrelated asset (Asset 1) are being unexpectedly merged, violating the expected allocation structure.

Context
In a test scenario involving two wallets (wlt_1 and wlt_2) and two distinct assets (contract_id_1 and contract_id_2):

1. After some transactions, wlt_1 holds allocations for Asset 2 (contract_id_2) as [issued_supply_2 - amount_3, amount_5] (two separate UTXOs).
2. A subsequent operation sends Asset 1 (contract_id_1) from wlt_1 to wlt_2.
3. After this send operation, the allocations for Asset 2 in wlt_1 are incorrectly merged into a single UTXO [issued_supply_2 - amount_3 + amount_5], causing an assertion failure.

Expected Behavior
Sending Asset 1 should not affect the UTXO structure of Asset 2. The allocations for Asset 2 in wlt_1 should remain as two separate entries ([issued_supply_2 - amount_3, amount_5]).

Observed Behavior
The UTXOs for Asset 2 are merged into one entry during the send operation for Asset 1, suggesting unintended interaction between asset allocations.

Reproduction Steps

1. Set up two wallets (wlt_1, wlt_2) and two asset contracts (contract_id_1, contract_id_2).
2. Perform cross-sends of assets between wallets.
3. After sending Asset 1, check wlt_1's allocations for Asset 2.

...
    wlt_2.send(&mut wlt_1, wout, contract_id_2, amount_5, sats, None);
    wlt_1.check_allocations(
        contract_id_1,
        asset_schema_1,
        vec![issued_supply_1 - amount_1 - amount_2, amount_4],
        true,
    );
    wlt_1.check_allocations(
        contract_id_2,
        asset_schema_2,
        vec![issued_supply_2 - amount_3, amount_5], // assertion passes
        true,
    );
    wlt_2.check_allocations(
        contract_id_1,
        asset_schema_1,
        vec![amount_1 + amount_2 - amount_4],
        false,
    );
    wlt_2.check_allocations(
        contract_id_2,
        asset_schema_2,
        vec![amount_3 - amount_5],
        false,
    );

    println!("-- DEBUG: wlt_1 spends asset 1, received back");
    let amount_6 = if asset_schema_1 == AssetSchema::Uda {
        1
    } else {
        issued_supply_1 - amount_1 - amount_2 + amount_4
    };
    sats -= 1000;
    // println!("before send, you can dump and debug now...");
    // std::thread::sleep(std::time::Duration::from_secs(30));
    wlt_1.send(&mut wlt_2, wout, contract_id_1, amount_6, sats, None);

    wlt_1.check_allocations(contract_id_1, asset_schema_1, vec![], false);
    wlt_1.check_allocations(
        contract_id_2,
        asset_schema_2,
        vec![issued_supply_2 - amount_3, amount_5], // assertion failes: actual allocation is vec![issued_supply_2 - amount_3 + amount_5]
        true,
    );
...