Position values when held after maturity should use vault share price at time of close

[dpaiton]

This is also described in delvtech/agent0#1683

Problem

When showing a user's position value after maturity the FE uses our hyperdrive-rs calculate_close_long to estimate the shares returned to the user. This uses the current vault share price and does not account for Hyperdrive auto-closing positions at maturity, which therefore fails to account for zombie interest going to the LPs.

Solution

Ideally we would account for checkpointing, auto-closing positions, and zombie interest in hyperdrive-rs itself (#23).

Until then, you can adjust the value reported to the user pretty easily. Using the share price at maturity (which can be obtained from the corresponding checkpoint event), calculation is user_return_in_shares = rust_shares_returned * maturity_share_price / current_share_price.

If the user wants base back, then you don't do the last conversion: user_return_in_base = rust_shares_returned * maturity_share_price.