Merge #21599: test: Replace file level integer overflow suppression with function level suppression

585854ac66a61fbb60849c2dfdd03f10b0150c75 test: Replace blanket UBSan signed integer overflow suppression for txmempool.cpp with specific suppression (practicalswift)

Pull request description:

  Replace file level (`txmempool.cpp`) signed integer overflow suppression with function level suppression (`CTxMemPool::PrioritiseTransaction`). The suppression was added yesterday in #21586.

  Rationale: To avoid risk hiding other signed integer overflows in `txmempool.cpp`.

  Obviously it would be better if this signed integer overflow fixed instead of suppressed - see details #20626. Any taker? :)

  To hit the issue via fuzzing:

  ```
  $ UBSAN_OPTIONS="print_stacktrace=1:halt_on_error=1:report_error_type=1" FUZZ=validation_load_mempool src/test/fuzz/fuzz
  INFO: Seed: 1184244493
  INFO: Loaded 1 modules   (634418 inline 8-bit counters): 634418 [0x55a09fdfbf98, 0x55a09fe96dca),
  INFO: Loaded 1 PC tables (634418 PCs): 634418 [0x55a09fe96dd0,0x55a0a08450f0),
  INFO:     1264 files found in mempool/
  INFO: -max_len is not provided; libFuzzer will not generate inputs larger than 1040698 bytes
  INFO: seed corpus: files: 1264 min: 1b max: 1040698b total: 15997133b rss: 197Mb
  txmempool.cpp:847:15: runtime error: signed integer overflow: -7211388903327006720 + -7211353718954917888 cannot be represented in type 'long'
      #0 0x55a09c3ce2d8 in CTxMemPool::PrioritiseTransaction(uint256 const&, long const&) /home/thomas/bitcoin/src/txmempool.cpp:847:15
  ```

ACKs for top commit:
  JeremyRubin:
    utACK 585854a
  hebasto:
    ACK 585854ac66a61fbb60849c2dfdd03f10b0150c75, I have reviewed the code and it looks OK, I agree it can be merged.

Tree-SHA512: 5a343f028c1e1a1aba3b51a0eced605849184891ffafecb3cd2b424c6cfea01afd7c2672274936b0bac646075ec066408a570bf6b34bc9b87399a53ce20d8a23

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