refactor, BlockManager: Replace fastprune from arg with options

Remove access to the global gArgs for the fastprune argument and
replace it by adding a field to the existing BlockManager Options
struct.

When running `clang-tidy-diff` on this commit, there is a diagnostic
error: `unknown type name 'uint64_t' [clang-diagnostic-error] uint64_t
prune_target{0};`, which is fixed by including cstdint.

This should eventually allow users of the BlockManager to not rely on
the global gArgs and instead pass in their own options.

src/kernel/blockmanager_opts.h

@@ -5,6 +5,8 @@
 #ifndef BITCOIN_KERNEL_BLOCKMANAGER_OPTS_H
 #define BITCOIN_KERNEL_BLOCKMANAGER_OPTS_H
 
+#include <cstdint>
+
 class CChainParams;
 
 namespace kernel {
@@ -16,6 +18,7 @@ namespace kernel {
 struct BlockManagerOpts {
     const CChainParams& chainparams;
     uint64_t prune_target{0};
+    bool fast_prune{false};
 };
 
 } // namespace kernel