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/node/blockmanager_args.cpp

@@ -31,6 +31,8 @@ std::optional<bilingual_str> ApplyArgsManOptions(const ArgsManager& args, BlockM
     }
     opts.prune_target = nPruneTarget;
 
+    if (auto value{args.GetBoolArg("-fastprune")}) opts.fast_prune = *value;
+
     return std::nullopt;
 }
 } // namespace node