feat: enhance remove liquidity function to handle surplus balances

[3esmit]

Summary

• update remove_liquidity to compute user payouts from the live vault balances while keeping pool reserve bookkeeping based on tracked reserves
• keep LP burn semantics unchanged by burning exactly the requested LP amount instead of the previous redundant delta_lp identity
• add unit and integration coverage for fee-surplus exits, actual-payout slippage checks, and reserve-vs-vault mismatch rejection

Fixes #15
Replaces logos-blockchain/logos-execution-zone#420

Testing

• cargo +1.94.0 test -p amm_program remove_liquidity
• RISC0_DEV_MODE=1 cargo +1.94.0 test -p integration_tests amm_remove_liquidity
• cargo +nightly fmt --all -- --check
• taplo fmt --check .
• RISC0_SKIP_BUILD=1 cargo +1.94.0 clippy --workspace --all-targets -- -D warnings
• RISC0_DEV_MODE=1 cargo +1.94.0 test --workspace --exclude integration_tests
• RISC0_DEV_MODE=1 cargo +1.94.0 test -p integration_tests

Notes

• remove-liquidity transfers now use each LP's pro-rata share of the actual vault holdings, so accumulated fee surplus is paid out on exit
• pool reserve_a and reserve_b remain reserve-based after exit, which preserves any remaining surplus as vault_balance - reserve for the LPs who stay in the pool
• remove-liquidity now rejects invalid states where a vault balance falls below its tracked reserve, matching the existing add/swap safety checks
• there are no Instruction, IDL, guest entrypoint, or account-schema changes in this PR

[Copilot]

Pull request overview

This PR updates AMM remove_liquidity to pay exiting LPs pro-rata from live vault balances (thereby distributing accumulated fee surplus), while keeping tracked reserves as the bookkeeping source-of-truth for pool reserves.

Changes:

• Compute remove-liquidity payouts from actual vault_a/vault_b token balances and run slippage checks against those actual payout amounts.
• Keep reserve accounting based on tracked reserves and add a guard that rejects vault_balance < tracked_reserve states.
• Simplify LP burn semantics to burn exactly the requested LP amount, and add unit + integration coverage for surplus exits and mismatch rejection.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
amm/src/remove.rs	Uses live vault balances for payout math + slippage checks; burns exact requested LP; asserts reserves do not exceed vault balances.
amm/src/tests.rs	Adds unit tests for reserve-vs-vault mismatch panics and surplus-based payout chained calls; updates expected transfer amounts.
integration_tests/tests/amm.rs	Adds an integration test covering surplus distribution on remove-liquidity and expected resulting vault/user balances.

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[0x-r4bbit]

As discussed in #12

Let's first clarify whether we want "recover surplus" in the first place.
Then we can discuss whether we want the changes here.

/cc @gravityblast

[0x-r4bbit]

Closing this for now as #38 has been closed as well.