Test insurance payout window circuit breaker

[Hibhee01]

Overview

Adds regression coverage for the insurance payout circuit breaker's per-pool rolling payout window.

Related Issue

Closes #1033

Changes

• Added helpers in the insurance circuit-breaker test module to create funded policies and process paid claims.
• Covered an accepted payout at the configured daily limit.
• Covered a second in-window payout rejected with DailyPayoutLimitExceeded.
• Covered window expiry resetting get_pool_window_payout and allowing a new payout.

Verification Results

• cargo +stable fmt -p propchain-insurance completed, with warnings because the repo's rustfmt config uses nightly-only options.
• git diff --check passed.
• cargo +stable test -p propchain-insurance could not complete locally because the Windows linker setup is missing MSVC system libraries for the repo-forced rust-lld linker:
  • rust-lld: error: could not open 'kernel32.lib': no such file or directory
  • same missing-library error for ntdll.lib, userenv.lib, ws2_32.lib, and dbghelp.lib

Acceptance Criteria

Criteria	Status
Payout under the limit is accepted	Done
Payout over the limit is rejected with DailyPayoutLimitExceeded	Done
Window rollover resets the accumulator	Done
cargo test -p propchain-insurance passes	Blocked locally by Windows linker environment

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