add MatchTypeCommandStartMaybeWithBotUsernameSuffix command match method

[Interstellar750]

Create a field name username in the Bot and handler structures to match commands like /command@username_bot.

Also created a bot.Username() string method to return the bot's username (without @).

When using bot.New() without bot.WithSkipGetMe() option, the username field is filling by following code:

func New(token string, options ...Option) (*Bot, error) {
	// other code...
	if !b.skipGetMe {
-		_, err := b.GetMe(ctx)
+		botInfo, err := b.GetMe(ctx)
		if err != nil {
			return nil, fmt.Errorf("error call getMe, %w", err)
		}
+		b.username = botInfo.Username
	}

	return b, nil
}

If with the bot.WithSkipGetMe() option, this match method will work the same as MatchTypeCommandStartOnly, then bot.Username() will return an empty string.

This PR may not be good. If you think it is not good, you can close it directly. Some issues mentioned that this is needed, or are there other better ways?

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 45.54%. Comparing base (a88fae3) to head (404d70c).

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #196      +/-   ##
==========================================
+ Coverage   45.31%   45.54%   +0.23%     
==========================================
  Files          29       29              
  Lines        2315     2325      +10     
==========================================
+ Hits         1049     1059      +10     
  Misses       1223     1223              
  Partials       43       43              

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[parmetra]

@Interstellar750 hello! Could you please tell why you closed this PR? I think it makes sense to reopen it and merge it into the main branch.
This feature is really useful - and it will work straight out of the box without any additional middleware.

[Interstellar750]

@parmetra Thank you for your attention.

I think this method is still somewhat problematic. IIt relies on the bot.GetMe() method call inside bot.New() function to fill the username field, but if the bot.WithSkipGetMe() option is used when creating the bot instance, this field will be empty and it will never work.

It doesn't guarantee it will work in both states, so I closed this PR.

A better approach is to create a package and store messages about the bot within it. When needed, import this package and read the username field for matching.

You might also need to use the bot.WithDefaultHandler() option to specify a handler to manually dispatch update and matching commands.