Fix typos and improve documentation clarity

[sergeypanin1994]

• Corrected spelling of 'exisiting' to 'existing'.
• Fixed 'depreciated' to 'deprecated'.
• Changed 'Dev's' to 'Devs' to correctly pluralize 'Dev'.
• Fixed 'its' to 'it's' where needed.
• Corrected 'checksummed' to 'checksumed' in the context of addresses with checksum.

These changes ensure better readability and accurate terminology in the documentation. Feel free to reach out if further assistance is needed.