[crac] RFR: API for restore time [v2]

[Anton Kozlov]

> This PR adds an ability to get restore time, similar to RuntimeMXBean.getUptime() [1] and getStartTime(). Before I used to print timestamps and parse console output, which was not very convenient.
> 
> [1] https://docs.oracle.com/en/java/javase/17/docs/api/java.management/java/lang/management/RuntimeMXBean.html#getUptime()

Anton Kozlov has updated the pull request incrementally with one additional commit since the last revision:

  Guarantee len

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Changes:
  - all: https://git.openjdk.org/crac/pull/29/files
  - new: https://git.openjdk.org/crac/pull/29/files/a57caf3c..54512e3d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=crac&pr=29&range=01
 - incr: https://webrevs.openjdk.org/?repo=crac&pr=29&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/crac/pull/29.diff
  Fetch: git fetch https://git.openjdk.org/crac pull/29/head:pull/29

PR: https://git.openjdk.org/crac/pull/29