Refactor identifier length validation in ics24 implementation

[mina86]

Firstly, remove asserts from the validate_identifier_length and
validate_prefix_length functions. Instead, let the regular checks
handle cases where min and max constraints don’t allow for a valid
prefix to exist.

Secondly, ensure minimum length constraints are at least one. This
makes sure that the validation functions will check for empty
identifiers and prefixes. This makes empty identifier check in
validate_channel_identifier as well as IdentifierError::Empty variant
unnecessary. We can get rid of those.

Lastly, collapse all checks in validate_prefix_length into a single
call to validate_identifier_length with correctly adjusted min and max
constraints.