Disable deduplication for summary mode

[Davidyz]

Deduplication doesn't play very nicely with summarysation due to the following:

1. it prevents the LLM requesting the same results without summarisation;
2. the summariser doesn't always produce the summary. Its system prompt instructs it to optimise the summary based on the query. When deduplication is on, the main chat LLM won't be able to see these.

Therefore, I'm disabling deduplication when summarisation is enabled.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.75%. Comparing base (99709a9) to head (e7a6074).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #223   +/-   ##
=======================================
  Coverage   99.75%   99.75%           
=======================================
  Files          21       21           
  Lines        1627     1627           
=======================================
  Hits         1623     1623           
  Misses          4        4           

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