Replace `scon` value parser with `scale_value` parser

[smiasojed]

Currently, both options are being used, each with similar functionality but employing slightly different grammar. This discrepancy requires RPC command parameters to be formatted differently from other commands.

scale_value parser: https://github.com/paritytech/scale-value/blob/372a74870d46f9b4d681807bdc8d49724abcdef4/src/string_impls/from_string.rs#L60

scon value parser: https://github.com/paritytech/cargo-contract/blob/3d74a06c62b664fe5e2d684a11b7f7b44cf65f63/crates/transcode/src/scon/parse.rs#L59