Fix compile on arm-linux-androideabi (32-bit) using a newer NDK

- @tobtoht reported err with size_t -> uint64_t
- Also address some PR comments (@vtnerd namespace comment +
@boog900 freeing unallocated rust type)
- Some cleaning

src/fcmp_pp/curve_trees.cpp

@@ -644,8 +644,7 @@ static typename fcmp_pp::curve_trees::LayerReduction<C_PARENT> get_next_layer_re
 // CurveTrees public member functions
 //----------------------------------------------------------------------------------------------------------------------
 template<>
-CurveTrees<Helios, Selene>::LeafTuple CurveTrees<Helios, Selene>::leaf_tuple(
+CurveTrees<Helios, Selene>::LeafTuple CurveTrees<Helios, Selene>::leaf_tuple(const OutputPair &output_pair) const
-    const OutputPair &output_pair) const
 {
     const crypto::public_key &output_pubkey = output_pair.output_pubkey;
     const rct::key &commitment              = output_pair.commitment;

src/fcmp_pp/curve_trees.h

@@ -164,7 +164,10 @@ template<typename C1, typename C2>
 class CurveTrees
 {
 public:
-    CurveTrees(std::unique_ptr<C1> &&c1, std::unique_ptr<C2> &&c2, const uint64_t c1_width, const uint64_t c2_width):
+    CurveTrees(std::unique_ptr<C1> &&c1,
+        std::unique_ptr<C2> &&c2,
+        const std::size_t c1_width,
+        const std::size_t c2_width):
             m_c1{std::move(c1)},
             m_c2{std::move(c2)},
             m_c1_width{c1_width},
@@ -240,7 +243,7 @@ public:
 //member functions
 public:
     // Convert output pairs into leaf tuples, from {output pubkey,commitment} -> {O,C} -> {O.x,I.x,C.x}
-    LeafTuple leaf_tuple(const OutputPair &outpout_pair) const;
+    LeafTuple leaf_tuple(const OutputPair &output_pair) const;
 
     // Flatten leaves [(O.x, I.x, C.x),(O.x, I.x, C.x),...] -> [O.x, I.x, C.x, O.x, I.x, C.x...]
     std::vector<typename C2::Scalar> flatten_leaves(std::vector<LeafTuple> &&leaves) const;

src/fcmp_pp/fcmp_pp_rust/fcmp++.h

@@ -1,10 +1,12 @@
-namespace fcmp_pp_rust {
 #include <cstdarg>
 #include <cstdint>
 #include <cstdlib>
 #include <ostream>
 #include <new>
 
+
+namespace fcmp_pp_rust
+{
 // ----- deps C bindings -----
 
 /// Inner integer type that the [`Limb`] newtype wraps.
@@ -137,5 +139,4 @@ CResult hash_trim_selene(SelenePoint existing_hash,
                                              SeleneScalar child_to_grow_back);
 
 } // extern "C"
-
+}//namespace fcmp_pp
-}

src/fcmp_pp/fcmp_pp_rust/src/lib.rs

@@ -152,6 +152,7 @@ pub extern "C" fn hash_grow_helios(
     if let Some(hash) = hash {
         CResult::ok(hash)
     } else {
+        // TODO: return defined error here: https://github.com/monero-project/monero/pull/9436#discussion_r1720477391
         CResult::err(())
     }
 }
@@ -174,6 +175,7 @@ pub extern "C" fn hash_trim_helios(
     if let Some(hash) = hash {
         CResult::ok(hash)
     } else {
+        // TODO: return defined error here: https://github.com/monero-project/monero/pull/9436#discussion_r1720477391
         CResult::err(())
     }
 }
@@ -196,6 +198,7 @@ pub extern "C" fn hash_grow_selene(
     if let Some(hash) = hash {
         CResult::ok(hash)
     } else {
+        // TODO: return defined error here: https://github.com/monero-project/monero/pull/9436#discussion_r1720477391
         CResult::err(())
     }
 }
@@ -218,6 +221,7 @@ pub extern "C" fn hash_trim_selene(
     if let Some(hash) = hash {
         CResult::ok(hash)
     } else {
+        // TODO: return defined error here: https://github.com/monero-project/monero/pull/9436#discussion_r1720477391
         CResult::err(())
     }
 }