[zk-token-sdk] replace hard-coded constants with constant variables (#32274)
* add ristretto and scalar byte length constants
* add serialization and deserialization helper functions
* remove hard-coded constants in the `sigma` module
* remove hard-coded constants in the `encryption` module
* remove hard-coded constants in the `zk-token-elgamal` module
* Apply suggestions from code review
Co-authored-by: Tyera <tyera@solana.com>
* fix docs for range proof constants
* Apply suggestions from code review
Co-authored-by: Tyera <tyera@solana.com>
* clippy
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Co-authored-by: Tyera <tyera@solana.com>