feat: decode base64 secrets

[Ramilito]

Added a base64 utility decoder. Added ft type for secret_desc Added enter keymap to decode line

Solves #144

[mosheavni]

why not use vim.base64? https://neovim.io/doc/user/lua.html#_vim.base64

[Ramilito]

why not use vim.base64? https://neovim.io/doc/user/lua.html#_vim.base64

lol indeed why not! Removed that horrible base64 decoder and using vim.base64 instead, thank you for the correction 🙏