fix: unescape literal \n sequences in Telegram message formatting

[ptone]

Message text arriving at the Telegram formatter can contain literal backslash-n escape sequences instead of actual newlines — either from JSON encoding round-trips (FormatForDelivery) or from shell arguments that don't interpret \n. Apply unescapeNewlines in FormatMessage and FormatMessageV2 so Telegram displays proper line breaks.

Closes #48

Fixes #<issue_number_goes_here>

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• Tests pass
• Appropriate changes to documentation are included in the PR

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[gemini-code-assist]

Code Review

This pull request introduces literal newline and tab unescaping for Telegram messages by adding an unescapeNewlines helper function and applying it in FormatMessage and FormatMessageV2. It also includes comprehensive unit tests to verify the new behavior. The review feedback suggests optimizing the unescapeNewlines function by defining the strings.Replacer as a package-level variable to avoid redundant allocations on every function call.

[gemini-code-assist]

Creating a new strings.Replacer on every call to unescapeNewlines is inefficient because it compiles the replacement patterns each time. Declaring the replacer as a package-level variable and reusing it avoids these allocations and improves performance.

Suggested change

	func unescapeNewlines(s string) string {
	return strings.NewReplacer(`\n`, "\n", `\t`, "\t").Replace(s)
	}
	var newlineReplacer = strings.NewReplacer("\\n", "\n", "\\t", "\t")
	func unescapeNewlines(s string) string {
	return newlineReplacer.Replace(s)
	}