Make linearly executing workers start at different positions

[nck-mlcnv]

This pull request makes changes so that multiple workers that execute the same queries linearly, start at different positions.
The starting positions are equally distanced from each other.

Query Handling Enhancements:

• src/main/java/org/aksw/iguana/cc/query/handler/QueryHandler.java: Added a totalWorkerCount field and a method to set this value. Updated the getQuerySelectorInstance method to use this field for the LinearQuerySelector initialization. [1] [2] [3]

Query Selector Improvements:

• src/main/java/org/aksw/iguana/cc/query/selector/impl/LinearQuerySelector.java: Modified the LinearQuerySelector to support an optional starting index and adjusted the getNextIndex and getCurrentIndex methods accordingly.

Worker Initialization Fixes:

• src/main/java/org/aksw/iguana/cc/tasks/impl/Stresstest.java: Updated the Stresstest class to initialize query handlers and count the number of workers for each query handler during both warmup and main execution phases. [1] [2] [3] [4]

Bug Fixes:

• src/main/java/org/aksw/iguana/cc/worker/impl/SPARQLProtocolWorker.java: Fixed a bug in the executeHttpRequest method to correctly use the querySelector's current index.

Testing Enhancements:

• src/test/java/org/aksw/iguana/cc/query/selector/impl/LinearQuerySelectorTest.java: Added a test case to verify the functionality of the LinearQuerySelector with a starting index.

[bigerl]

Thx for the PR. Changes look mostly good. There is just one spot where I am a little confused. Only, I am not too fond of the -1 initialization of getCurrentIndex(). Still, I don't have a better solution at hand ATM.