Merge bitcoin/bitcoin#30742: kernel: Use spans instead of vectors for passing block headers to validation functions

a2955f0979 validation: Use span for ImportBlocks paths (TheCharlatan)
20515ea3f5 validation: Use span for CalculateClaimedHeadersWork (TheCharlatan)
52575e96e7 validation: Use span for ProcessNewBlockHeaders (TheCharlatan)

Pull request description:

  Makes it friendlier for potential future users of the kernel library if they do not store the headers in a std::vector, but can guarantee contiguous memory.

  Take this opportunity to also change the argument of ImportBlocks previously taking a `std::vector` to a `std::span`.

ACKs for top commit:
  stickies-v:
    re-ACK a2955f0979 - no changes except further walking the ~file~ path of modernizing variable names.
  maflcko:
    ACK a2955f0979 🕑
  achow101:
    ACK a2955f0979
  danielabrozzoni:
    ACK a2955f0979

Tree-SHA512: 8b07f4ad26e270b65600d1968cd78847b85caca5bfbb83fd9860389f26656b1d9a40b85e0990339f50403d18cedcd2456990054f3b8b0bedce943e50222d2709

src/node/blockstorage.cpp

@@ -1210,7 +1210,7 @@ public:
     }
 };
 
-void ImportBlocks(ChainstateManager& chainman, std::vector<fs::path> vImportFiles)
+void ImportBlocks(ChainstateManager& chainman, std::span<const fs::path> import_paths)
 {
     ImportingNow imp{chainman.m_blockman.m_importing};
 
@@ -1245,7 +1245,7 @@ void ImportBlocks(ChainstateManager& chainman, std::vector<fs::path> vImportFile
     }
 
     // -loadblock=
-    for (const fs::path& path : vImportFiles) {
+    for (const fs::path& path : import_paths) {
         AutoFile file{fsbridge::fopen(path, "rb")};
         if (!file.IsNull()) {
             LogPrintf("Importing blocks file %s...\n", fs::PathToString(path));