refactor: add LIFETIMEBOUND to blockfilter where needed

Ensure that the return values do not have a lifetime that exceeds
the lifetime of what it is bound to.
See https://github.com/bitcoin/bitcoin/blob/master/doc/developer-notes.md#lifetimebound

Author: stickies-v

src/blockfilter.h

@@ -11,6 +11,7 @@
 #include <unordered_set>
 #include <vector>
 
+#include <attributes.h>
 #include <primitives/block.h>
 #include <serialize.h>
 #include <uint256.h>
@@ -65,8 +66,8 @@ class GCSFilter
     GCSFilter(const Params& params, const ElementSet& elements);
 
     uint32_t GetN() const { return m_N; }
-    const Params& GetParams() const { return m_params; }
-    const std::vector<unsigned char>& GetEncoded() const { return m_encoded; }
+    const Params& GetParams() const LIFETIMEBOUND { return m_params; }
+    const std::vector<unsigned char>& GetEncoded() const LIFETIMEBOUND { return m_encoded; }
 
     /**
      * Checks if the element may be in the set. False positives are possible
@@ -128,10 +129,10 @@ class BlockFilter
     BlockFilter(BlockFilterType filter_type, const CBlock& block, const CBlockUndo& block_undo);
 
     BlockFilterType GetFilterType() const { return m_filter_type; }
-    const uint256& GetBlockHash() const { return m_block_hash; }
-    const GCSFilter& GetFilter() const { return m_filter; }
+    const uint256& GetBlockHash() const LIFETIMEBOUND { return m_block_hash; }
+    const GCSFilter& GetFilter() const LIFETIMEBOUND { return m_filter; }
 
-    const std::vector<unsigned char>& GetEncodedFilter() const
+    const std::vector<unsigned char>& GetEncodedFilter() const LIFETIMEBOUND
     {
         return m_filter.GetEncoded();
     }

src/index/blockfilterindex.h

@@ -5,6 +5,7 @@
 #ifndef BITCOIN_INDEX_BLOCKFILTERINDEX_H
 #define BITCOIN_INDEX_BLOCKFILTERINDEX_H
 
+#include <attributes.h>
 #include <blockfilter.h>
 #include <chain.h>
 #include <flatfile.h>
@@ -49,9 +50,9 @@ class BlockFilterIndex final : public BaseIndex
 
     bool CustomRewind(const interfaces::BlockKey& current_tip, const interfaces::BlockKey& new_tip) override;
 
-    BaseIndex::DB& GetDB() const override { return *m_db; }
+    BaseIndex::DB& GetDB() const LIFETIMEBOUND override { return *m_db; }
 
-    const char* GetName() const override { return m_name.c_str(); }
+    const char* GetName() const LIFETIMEBOUND override { return m_name.c_str(); }
 
 public:
     /** Constructs the index, which becomes available to be queried. */