fix(peerfinder): include the header that declares SlotCensus

The phase-10 merge relocated PeerFinder's Manager interface from
src/xrpld/peerfinder/ to include/xrpl/peerfinder/, and SlotCensus moved with it
so libxrpl could see it. Logic.h uses SlotCensus as the return type of
getSlotCensus() but was never given the include, so every build failed:

  build/modules/xrpl.libxrpl.peerfinder/xrpl/peerfinder/detail/Logic.h:192:5:
    error: unknown type name 'SlotCensus'
  ...:197:16: error: use of undeclared identifier 'SlotCensus'; did you mean
    'getSlotCensus'?

That single missing declaration was the whole failure. The 34 further errors in
the log were cascade: PeerFinderTest could not compile, so every TEST() in
src/tests/libxrpl/peerfinder/PeerFinder.cpp failed to instantiate against
gtest-internal.h. All four platforms (ubuntu-clang, ubuntu-gcc, macos-arm64,
windows-amd64) and clang-tidy reported the same root cause.

No include cycle: PeerfinderManager.h does not include detail/Logic.h, directly
or transitively. Levelization is unchanged because both headers are already in
xrpl.libxrpl.peerfinder, so generate.py produces no diff.

This is the risk called out when the merge landed -- moving SlotCensus into the
public header was the one resolution a static check could not confirm, and only
a compile would prove it. CI is that compile, and it found this.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

include/xrpl/peerfinder/detail/Logic.h

@@ -11,6 +11,7 @@
 #include <xrpl/beast/utility/WrappedSink.h>
 #include <xrpl/beast/utility/instrumentation.h>
 #include <xrpl/peerfinder/Config.h>
+#include <xrpl/peerfinder/PeerfinderManager.h>
 #include <xrpl/peerfinder/Slot.h>
 #include <xrpl/peerfinder/Types.h>
 #include <xrpl/peerfinder/detail/Bootcache.h>