doc: use proper doxygen formatting for CTxMemPool::cs #30504

1. 
   vasild commented at 10:28 am on July 23, 2024: contributor

   Having @par title followed by an empty line renders improperly in Doxygen - it results in a paragraph with a title but without a body.

   https://www.doxygen.nl/manual/commands.html#cmdpar

   This also results in a compiler warning (or error) with Clang 19:

   0./txmempool.h:368:34: error: empty paragraph passed to '@par' command [-Werror,-Wdocumentation]
   1  368 |      * [@par](/bitcoin-bitcoin/contributor/par/) Consistency guarantees
   2      |        ~~~~~~~~~~~~~~~~~~~~~~~~~~^
   31 error generated.
   

2. doc: use proper doxygen formatting for CTxMemPool::cs

   Having `@par title` followed by an empty line renders improperly in
   Doxygen - it results in a paragraph with a title but without a body.
   
   https://www.doxygen.nl/manual/commands.html#cmdpar
   
   This also results in a compiler warning (or error) with Clang 19:
   
   ```
   ./txmempool.h:368:34: error: empty paragraph passed to '@par' command [-Werror,-Wdocumentation]
     368 |      * @par Consistency guarantees
         |        ~~~~~~~~~~~~~~~~~~~~~~~~~~^
   1 error generated.
   ```

   6a5e9e40e1
3. 
   DrahtBot commented at 10:28 am on July 23, 2024: contributor

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4. DrahtBot added the label Docs on Jul 23, 2024
5. 
   maflcko commented at 10:43 am on July 23, 2024: member

   review ACK 6a5e9e40e1dd3d397020703feb9aa0b6f4577c98
6. tdb3 approved
7. 
   tdb3 commented at 10:49 am on July 23, 2024: contributor

   ACK 6a5e9e40e1dd3d397020703feb9aa0b6f4577c98 Looks to be rendered correctly now:

   

8. fanquake merged this on Jul 23, 2024
9. fanquake closed this on Jul 23, 2024

   ---

10. vasild deleted the branch on Jul 23, 2024

Contributors
vasild DrahtBot maflcko tdb3

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