Replace the hardcoded numeric byte-stream seeds ([0; 32], [1; 32], ...)
used for domain separation in PDA derivation with descriptive byte-string
constants, mirroring the AMM config account's existing b"CONFIG" seed.
amm: [0; 32] -> b"LIQUIDITY_TOKEN"
[1; 32] -> b"LP_LOCK_HOLDING"
stablecoin: [0; 32] -> b"POSITION"
[1; 32] -> b"POSITION_VAULT"
twap_oracle: [2; 32] -> b"PRICE_OBSERVATIONS"
[3; 32] -> b"ORACLE_PRICE_ACCOUNT"
[4; 32] -> b"CURRENT_TICK_ACCOUNT"
Since the seeds are now variable-length, each compute_*_pda_seed function
builds its hash input with a Vec and extend_from_slice instead of a
fixed-size buffer with offset writes.
Closes#146
Andrea Franz