add max total stake cap

[EDOHWARES]

Summary

This PR adds an optional maximum total liquidity cap for prediction pools. Pool creators can set a max_total_stake limit (with 0 meaning “no cap”). Once the cap is reached, further predictions are rejected to prevent additional liquidity from entering the market. The pool creator can increase the cap (or remove it by setting to 0) before the market ends.

Changes

• Pool struct

  • Added max_total_stake: i128 to Pool
  • Default value set to 0 in create_pool to preserve existing behavior (unlimited cap)

• Prediction placement

  • Updated place_prediction to enforce the global cap:
    • If max_total_stake > 0 and total_stake + amount > max_total_stake, the call aborts with PredifiError::MaxTotalStakeExceeded

• Cap management

  • Added increase_max_total_stake(env, creator, pool_id, new_max_total_stake):
    • Creator-only
    • Only allowed while pool is active and before end_time
    • Must be >= current total_stake
    • Only allows increasing (or setting unlimited 0)

• Errors

  • Added PredifiError::MaxTotalStakeExceeded = 104

Behavior Notes

• Existing pools and flows remain unchanged unless the cap is explicitly increased/set.
• Cap is applied globally at the pool level (across all outcomes).

Testing

• No new tests were added in this minimal implementation; existing compilation diagnostics show

Closes #322

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[EDOHWARES]

@Yunusabdul38 , pls review PR

[Yunusabdul38]

LGTM