fix: increase loadable epub size (#1638)

## Summary

* **What is the goal of this PR?** Slightly increase the OOM limit when
loading epubs
* **What changes are included?** Switched vectors for parsing epubs to
deques, allowing use of more memory

## Additional Context

* Increases loadable epub size from 2000+ chapter/ToC entries loadable
to 5000+ chapter/ToC entries
* #1574, but without the complicated stuff

---

### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _**NO**_

### Testing
| Commit | Book | Time |
|----------|------|-------|
| 83cd96bc2f | 1000.epub | ~30 sec |
| 83cd96bc2f | 5000.epub | crash |
| PR | 1000.epub | ~29 sec |
| PR | 5000.epub | ~2 min 20 sec |

=> No actual loading time regressions

[tested_epubs.zip](https://github.com/user-attachments/files/26645243/tested_epubs.zip)

lib/Epub/Epub/BookMetadataCache.h

@@ -3,8 +3,8 @@
 #include <HalStorage.h>
 
 #include <algorithm>
+#include <deque>
 #include <string>
-#include <vector>
 
 class BookMetadataCache {
  public:
@@ -61,7 +61,7 @@ class BookMetadataCache {
     uint16_t hrefLen;   // length for collision reduction
     int16_t spineIndex;
   };
-  std::vector<SpineHrefIndexEntry> spineHrefIndex;
+  std::deque<SpineHrefIndexEntry> spineHrefIndex;
   bool useSpineHrefIndex = false;
 
   static constexpr uint16_t LARGE_SPINE_THRESHOLD = 400;