RFR: 5700: Improve file and socket IO rule result texts

[Jean-Philippe Bempel]

Add new information along with longest event:
 - report the total and average pauses for the entire recording.
 - report the sum of all IO events for that file or host of the longest event
Add also some mock classes for IItemCollection with some mock events

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Commit messages:
 - 5700: Improve file and socket IO rule result texts

Changes: https://git.openjdk.java.net/jmc/pull/138/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=138&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-5700
  Stats: 463 lines in 12 files changed: 444 ins; 0 del; 19 mod
  Patch: https://git.openjdk.java.net/jmc/pull/138.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/138/head:pull/138

PR: https://git.openjdk.java.net/jmc/pull/138