Fix three bugs: pop() return type, fill() cursor reset, and comment errors

This commit addresses three bugs found in the circular buffer implementation:

1. Type Safety Bug - pop() return type (HIGH severity)
   - Changed pop() return type from 'T | undefined' to 'T'
   - The method never returns undefined; it either returns T or throws RangeError
   - Previous type signature was misleading and could cause incorrect null checks
   - Affects: src/ts/circular_buffer.ts:708

2. Consistency Bug - fill() missing cursor reset (MEDIUM severity)
   - Added 'this._cursor = 0' to fill() method
   - Now consistent with similar buffer-reorganizing methods (reverse, every, some)
   - Previously left internal rotation state unnormalized after filling
   - Affects: src/ts/circular_buffer.ts:501

3. Documentation Bug - copy-paste comment errors (LOW severity)
   - Fixed comment in some() that incorrectly said "every can mutate"
   - Fixed typo "_this.offset" → "this._offset"
   - Comments were copied from every() method and not updated
   - Affects: src/ts/circular_buffer.ts:611, 616

All tests pass (84/84) with 100% coverage maintained.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: StoneCypher

package-lock.json

@@ -498,6 +498,7 @@ class circular_buffer<T> {
     }
 
     this._length = this._capacity;
+    this._cursor = 0;
 
     return this._values;
 
@@ -607,12 +608,12 @@ class circular_buffer<T> {
     const normalized = this.toArray(),
           res        = normalized.some(functor, thisArg);
 
-    // every can mutate, so, store the result, which will usually be nothing
+    // some can mutate, so, store the result, which will usually be nothing
 
     this._values        = normalized;
     this._values.length = this._capacity;   // stack with new empties
     this._cursor        = 0;                // accomodate internal rotation
-    // do not mutate _this.offset; it doesn't change
+    // do not mutate this._offset; it doesn't change
 
     return res;
 
@@ -705,7 +706,7 @@ class circular_buffer<T> {
    *
    */
 
-  pop(): T | undefined {
+  pop(): T {
 
     if (this._length <= 0) {
       throw new RangeError(`Cannot pop, structure is empty`);