refactor: Removed redundant FsFile close() calls (#1434)

## Summary

**What is the goal of this PR?** (e.g., Implements the new feature for
file uploading.)

`DESTRUCTOR_CLOSES_FILE=1` is set in platformio.ini, which makes SdFat's
FsBaseFile destructor call close() automatically when a file goes out of
scope.

Three categories of file close calls remain untouched:
1. Close before Storage.remove() on the same path: ScreenshotUtil.cpp
closes the file before deleting it on write error. The remove might fail
if the file is still open.
2. Close before reopening the same variable: Epub.cpp writes a temp
NCX/nav file, closes it, then reopens it for reading. The
RecentBooksStore.cpp close before saveToFile() is the same pattern, it
rewrites the same file.
3. Close on member variables: BookMetadataCache.cpp (bookFile,
spineFile, tocFile), Section.cpp (file), XtcParser.cpp (m_file),
ZipFile.cpp (file). These persist beyond any single function scope, so
the destructor timing doesn't match the intended close point.

---

### 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? _**PARTIALLY**_

lib/Epub/Epub/css/CssParser.cpp

@@ -743,7 +743,6 @@ bool CssParser::saveToCache() const {
   }
 
   LOG_DBG("CSS", "Saved %u rules to cache", ruleCount);
-  file.close();
   return true;
 }
 
@@ -765,6 +764,7 @@ bool CssParser::loadFromCache() {
   if (file.read(&version, 1) != 1 || version != CssParser::CSS_CACHE_VERSION) {
     LOG_DBG("CSS", "Cache version mismatch (got %u, expected %u), removing stale cache for rebuild", version,
             CssParser::CSS_CACHE_VERSION);
+    // Explicitly close() file before calling Storage.remove()
     file.close();
     Storage.remove((cachePath + rulesCache).c_str());
     return false;
@@ -773,14 +773,12 @@ bool CssParser::loadFromCache() {
   // Read rule count
   uint16_t ruleCount = 0;
   if (file.read(&ruleCount, sizeof(ruleCount)) != sizeof(ruleCount)) {
-    file.close();
     return false;
   }
 
   if (ruleCount > MAX_RULES) {
     LOG_DBG("CSS", "Invalid cache rule count (%u > %zu)", ruleCount, MAX_RULES);
     rulesBySelector_.clear();
-    file.close();
     return false;
   }
 
@@ -799,19 +797,16 @@ bool CssParser::loadFromCache() {
     uint16_t selectorLen = 0;
     if (!hasRemainingBytes(sizeof(selectorLen))) {
       rulesBySelector_.clear();
-      file.close();
       return false;
     }
     if (file.read(&selectorLen, sizeof(selectorLen)) != sizeof(selectorLen)) {
       rulesBySelector_.clear();
-      file.close();
       return false;
     }
 
     if (selectorLen == 0 || selectorLen > MAX_SELECTOR_LENGTH || !hasRemainingBytes(selectorLen)) {
       LOG_DBG("CSS", "Invalid selector length in cache: %u", selectorLen);
       rulesBySelector_.clear();
-      file.close();
       return false;
     }
 
@@ -819,14 +814,12 @@ bool CssParser::loadFromCache() {
     selector.resize(selectorLen);
     if (file.read(&selector[0], selectorLen) != selectorLen) {
       rulesBySelector_.clear();
-      file.close();
       return false;
     }
 
     if (!hasRemainingBytes(CSS_FIXED_STYLE_BYTES)) {
       LOG_DBG("CSS", "Truncated CSS cache while reading style payload");
       rulesBySelector_.clear();
-      file.close();
       return false;
     }
 
@@ -836,28 +829,24 @@ bool CssParser::loadFromCache() {
 
     if (file.read(&enumVal, 1) != 1) {
       rulesBySelector_.clear();
-      file.close();
       return false;
     }
     style.textAlign = static_cast<CssTextAlign>(enumVal);
 
     if (file.read(&enumVal, 1) != 1) {
       rulesBySelector_.clear();
-      file.close();
       return false;
     }
     style.fontStyle = static_cast<CssFontStyle>(enumVal);
 
     if (file.read(&enumVal, 1) != 1) {
       rulesBySelector_.clear();
-      file.close();
       return false;
     }
     style.fontWeight = static_cast<CssFontWeight>(enumVal);
 
     if (file.read(&enumVal, 1) != 1) {
       rulesBySelector_.clear();
-      file.close();
       return false;
     }
     style.textDecoration = static_cast<CssTextDecoration>(enumVal);
@@ -880,7 +869,6 @@ bool CssParser::loadFromCache() {
         !readLength(style.paddingBottom) || !readLength(style.paddingLeft) || !readLength(style.paddingRight) ||
         !readLength(style.imageHeight) || !readLength(style.imageWidth)) {
       rulesBySelector_.clear();
-      file.close();
       return false;
     }
 
@@ -888,7 +876,6 @@ bool CssParser::loadFromCache() {
     uint8_t displayVal;
     if (file.read(&displayVal, 1) != 1) {
       rulesBySelector_.clear();
-      file.close();
       return false;
     }
     style.display = static_cast<CssDisplay>(displayVal);
@@ -897,7 +884,6 @@ bool CssParser::loadFromCache() {
     uint16_t definedBits = 0;
     if (file.read(&definedBits, sizeof(definedBits)) != sizeof(definedBits)) {
       rulesBySelector_.clear();
-      file.close();
       return false;
     }
     style.defined.textAlign = (definedBits & 1 << 0) != 0;
@@ -921,6 +907,5 @@ bool CssParser::loadFromCache() {
   }
 
   LOG_DBG("CSS", "Loaded %u rules from cache", ruleCount);
-  file.close();
   return true;
 }