fs: expose FileHandle class and add isFileHandle method

[amyssnippet]

This PR exposes the FileHandle class in node:fs and node:fs/promises, allowing developers to reliably check if an object is a file handle using instanceof or the new static helper method. Previously, FileHandle was hidden, forcing developers to rely on "duck typing" (checking for .fd and .close properties), which is unreliable.

Changes:

• exported FileHandle in lib/internal/fs/promises.js.
• Lazy-loads and exports FileHandle in lib/fs.js.
• Added a static FileHandle.isFileHandle(value) method.
• Added comprehensive tests in test/parallel/test-fs-filehandle-accessibility.js.

Fixes: #61637

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.73%. Comparing base (8e41b8d) to head (75b79e4).
⚠️ Report is 19 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #61650      +/-   ##
==========================================
- Coverage   89.74%   89.73%   -0.02%     
==========================================
  Files         674      674              
  Lines      204348   204381      +33     
  Branches    39271    39270       -1     
==========================================
+ Hits       183396   183401       +5     
- Misses      13262    13296      +34     
+ Partials     7690     7684       -6     

Files with missing lines	Coverage Δ
lib/fs.js	98.19% <100.00%> (+<0.01%)	⬆️
lib/internal/fs/promises.js	98.73% <100.00%> (+<0.01%)	⬆️

... and 37 files with indirect coverage changes

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[amyssnippet]

the Ci failure on macos is because of a recent commit that increased the debugger timeout on macOS from 10s to 15s due to known timing issues. The error shows it's still timing out at 15s, suggesting the flakiness persists.

Commit Details:

amol@Amols-MBP node %  git show 2bda7cbfb62
commit 2bda7cbfb62778bd793fbceaa9a5a907c3d344be
Author: Chengzhong Wu <[email protected]>
Date:   Fri Oct 24 10:21:32 2025 -0400

    test: increase debugger waitFor timeout on macOS
    
    PR-URL: https://github.com/nodejs/node/pull/60367
    Refs: https://github.com/nodejs/node/actions/runs/18694915575/job/53309761263?pr=60343
    Reviewed-By: Colin Ihrig <[email protected]>
    Reviewed-By: Luigi Pinca <[email protected]>
    Reviewed-By: Joyee Cheung <[email protected]>

diff --git a/test/common/debugger.js b/test/common/debugger.js
index 1a258913e00..f5a47cbe06e 100644
--- a/test/common/debugger.js
+++ b/test/common/debugger.js
@@ -7,12 +7,10 @@ const BREAK_MESSAGE = new RegExp('(?:' + [
   'exception', 'other', 'promiseRejection', 'step',
 ].join('|') + ') in', 'i');
 
-// Some macOS machines require more time to receive the outputs from the client.
 let TIMEOUT = common.platformTimeout(10000);
-if (common.isWindows) {
-  // Some of the windows machines in the CI need more time to receive
-  // the outputs from the client.
-  // https://github.com/nodejs/build/issues/3014
+// Some macOS and Windows machines require more time to receive the outputs from the client.
+// https://github.com/nodejs/build/issues/3014
+if (common.isWindows || common.isMacOS) {
   TIMEOUT = common.platformTimeout(15000);
 }

[bakkot]

instanceof is not an appropriate way to check class membership. E.g.:

> require('vm').runInNewContext('[]') instanceof Array
false

[amyssnippet]

instanceof is not an appropriate way to check class membership. E.g.:

> require('vm').runInNewContext('[]') instanceof Array
false

i have seen there is a pattern in nodejs classes and i will update my function to follow it! thank you