Let LongBridge sell BOXX when buying power is short

[Pigbibi]

Adjust the LongBridge execution flow so the cash-sweep symbol can be sold even when the underweight candidate is smaller than one share and buying power is short.

This keeps the platform from getting stuck holding BOXX when the strategy wants to move into SOXL/SOXX but only a partial position can be funded on the current run.

Tests:

• PYTHONPATH=/home/ubuntu/Projects/QuantPlatformKit/src:/home/ubuntu/Projects/UsEquityStrategies/src python3 -m pytest tests/test_rebalance_service.py -k cash_sweep -q
• python3 -m py_compile application/execution_service.py tests/test_rebalance_service.py

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Do not force BOXX sale when funding need is zero

When cash_sweep_sale_quantity_to_fund_buy(...) returns 0 (for example, because current investable cash already covers the next buy), this branch overwrites it to 1 and still submits a BOXX sell. In execute_rebalance_cycle, that means any cycle with a buy candidate and sellable BOXX can generate an unnecessary market sell even though no additional funding is needed, causing avoidable churn and allocation drift.

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