Address clang-tidy findings in //content/browser/interest_group

* Prevent UB division by zero with a CHECK. Perhaps impossible at
  runtime, but I am choosing to be pedantic.
  https://timsong-cpp.github.io/cppwp/n4659/expr.mul

* Fix accidental use-after-move in InterestGroupAuctionReporter
  constructor. Not sure if the behavior is defined.

* Some return values are currently only used when DCHECK is enabled.
  Style guide prefers CHECK anyway, so I'm upgrading the DCHECKs to
  CHECKs rather than adding [[maybe_unused]] annotations.

  Relevant section from chromium C++ style guide:
  https://chromium.googlesource.com/chromium/src/+/main/styleguide/c++/c++.md#check_dcheck_notreached_noreturn_and-notreached

Change-Id: Idef64ef13fe1b7fc386f6b102bc81f9513ffb0ee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5254560
Commit-Queue: Dan McArdle <dmcardle@chromium.org>
Reviewed-by: Maks Orlovich <morlovich@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1255166}

• content/browser/interest_group/auction_process_manager.cc[diff]
• content/browser/interest_group/bidding_and_auction_serializer.cc[diff]
• content/browser/interest_group/debuggable_auction_worklet_tracker.cc[diff]
• content/browser/interest_group/interest_group_auction_reporter.cc[diff]