Increase max allowed characters in `TokenSymbol`

[PhilippGackstatter]

Right now, TokenSymbol allows a maximum of 6 ASCII characters, which is 48 bits. Below I’ve listed the maximum allowed token symbol length on different blockchains. This might be “a separate discussion,” but if we increase TokenSymbol to a maximum of 8 characters (8 ASCII characters), it would still fit within a single field element, while being noticeably less restrictive. For that reason, I suggest increasing the symbol length to 8 characters.

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I think using just uppercase characters is fine! Increasing the character length to fit into a one field elements would be ideal in my opinion.

Since the encoding will be the upper characters, I think we would fit 12 upper-case letters with the following maximum encoding value if I didn't miscalculate

pub const MAX_ENCODED_VALUE: u64 = 2481152873203736562;

Originally posted by @onurinanc in #2344

[Farukest]

I got this @PhilippGackstatter need assign and review if jump in is okay :)