Fusionner automatiquement les doubles posts 2.4.0

• Fixed a bug where messages would not merge when the message length limit was disabled.
• Fixed a bug in the regular expression where merging of quoted messages was prohibited.
• Added a check to ensure that the "[automerge]" tag contains nothing but a timestamp.
• Added handling of the maximum number of attachments in a message.
• Code refactoring.

Fixed a bug when merging messages when a message is not sent on the last page.

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