[core] Speed up NCZBLOCK reads and skip double AES for pre-decrypted NCZ (#4582)

- [x] I have read and followed the [Contribution Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/CONTRIBUTING.md#code-contributions).
- [x] I have read and followed the [AI Policy](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/AI.md).
- [x] I have read and followed the [Coding Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/Coding.md) to the best of my ability.

-------------------
- Use a 32-slot direct-mapped block cache and reuse one ZSTD_DCtx per
  BlockReader instead of re-creating it per block.
- Find the covering section with std::lower_bound instead of a linear scan
  (helps BKTR updates with thousands of sections).
- Mark BlockNczFile as HasDecryptedSections() and drop its CTR pass; NCZ
  body is stored decrypted, so NcaFileSystemDriver now skips its AES layers
  for these files (no double decryption).
- Recognize .xcz as XCZ in AppLoader_XCI::IdentifyType.

thanks Reikatari

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4582
Reviewed-by: Maufeat <sahyno1996@gmail.com>

src/core/loader/xci.cpp

@@ -54,7 +54,8 @@ FileType AppLoader_XCI::IdentifyType(const FileSys::VirtualFile& xci_file) {
     // Identify XCI as a valid container even when it does not include a bootable Program NCA.
     // Bootability is handled by AppLoader_XCI::Load().
     if (xci.GetSecurePartitionNSP() != nullptr) {
-        return FileType::XCI;
+        return xci_file->GetName().ends_with(".xcz") ? FileType::XCZ
+                                                     : FileType::XCI;
     }
 
     return FileType::Error;