feat: Implement Consumer.offsetsForTimes

[tmdiep]

Retrieves cursors for timestamps from the TopicStatsClient to implement PubsubLiteConsumer.offsetsForTimes.

[codecov]

Codecov Report

Merging #123 (d8eda8d) into master (5135c6b) will increase coverage by 0.74%.
The diff coverage is 89.47%.

❗ Current head d8eda8d differs from pull request most recent head 591f4cb. Consider uploading reports for the commit 591f4cb to get more accurate results

@@             Coverage Diff              @@
##             master     #123      +/-   ##
============================================
+ Coverage     67.13%   67.87%   +0.74%     
- Complexity      131      136       +5     
============================================
  Files            10       10              
  Lines           642      660      +18     
  Branches         23       25       +2     
============================================
+ Hits            431      448      +17     
- Misses          201      202       +1     
  Partials         10       10              

Impacted Files	Coverage Δ	Complexity Δ
...gle/cloud/pubsublite/kafka/PubsubLiteConsumer.java	77.99% <89.47%> (+1.22%)	66.00 <5.00> (+5.00)

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[tmdiep]

Delaying merge until the RPC is publicly visible.

[tmdiep]

ComputeTimeCursor is now publicly visible.