colorize_nicks.py 33: add many improvements, features, and fixes

Changes:

- Remove the VALID_NICK regex to not be dependent on RFC spec and change
  the loop to split only on spaces, so the nick regex is free to match
  any suffix.

- Add nick_prefixes and nick_suffixes options to configure charset
  affixes.

- Replace the default 'greedy' matching with improved 'lazy' matching,
  because 'greedy' matches nicks incorrectly and crashes weechat. Thus
  remove ignore_nicks_in_urls option, since 'lazy' matching does not
  match nicks in substrings.

  closes #133 and #197.

  Rationale:

  - The greedy matching code recolors duplicated strings because of the
    way replace() works, so it crashes weechat on multiple duplicated
    nicks.

  - #259 does not really prevent that, since it can still be reproduced
    by mentioning a short nick e.g. F1, repeatedly in a message.

  - It can be fixed by iterating on unique words, but it still colorizes
    nicks in substrings if a nick is mentioned before (e.g. alice
    https://www.alice.com), hence the option ignore_nicks_in_urls fails.

- Replace hook_modifier() with hook_line() for a more granular parsing
  (e.g. prefix is separated from message, get filtered lines, etc).

  closes #70, closes #135.

- Add preserving of message colors logic. closes #49, closes #175.

- Add irc_only option to ignore non IRC messages (i.e. set buffer
  restrictions: plugin = irc, tags = irc_privmsg and irc_notice,
  type = channel and private).

- Add do not colorize nicks in filtered messages, and colorize_filtered
  option.

- Add colorizing of IRC prefixes and nicks on IRC private buffers.

- Update colorized_input_cb()  with the changes, and add decoding of IRC
  colors from input.

- Update config_init() parsing of options.

- Remove 'so,root' from blacklist_nicks default option. (These nicks do
  not make sense for defaults.)

- Change min_nick_length default option to 1. (Single char nicks should
  not be excluded by default.)

- Remove hook_modifier() that has the modifier colorize_nicks. (Is it
  possible to pass custom modifiers?)

- Replace % formatting strings with f-strings, " with ', and some code
  to use the := operator.

- Update identifiers, comments, and add some whitespace in code for
  readability.

- Remove unused global keywords and add error handlings.

- Remove utf-8 encoding header, add SPDX copyright + license tags, and
  add upstream link.

Author: ryoskzypu