refactor(collection): `!` overrides for unchecked iterator access

[Renegade334]

Please describe the changes this PR makes and why it should be merged:

Currently, for backward compatibility reasons, when manually traversing builtin iterators, the type of Iterator<T>.next().value resolves to T | any, or in other words, just any.

Under changes to iterators currently being planned for TypeScript 5.6, the resolved value type will change from any to T | void in strict mode.

There are a few instances in collection.ts where a result value no longer being any will cause issues. A test build shows the following errors:

src/collection.ts:86:29 - error TS2322: Type 'void | Value' is not assignable to type 'Value | Value[] | undefined'.
  Type 'void' is not assignable to type 'Value | Value[] | undefined'.

86   if (amount === undefined) return this.values().next().value;
                               ~~~~~~

src/collection.ts:90:54 - error TS2322: Type 'void | Value' is not assignable to type 'Value'.
  'Value' could be instantiated with an arbitrary type which could be unrelated to 'void | Value'.

90   return Array.from({ length: amount }, (): Value => iter.next().value);
                                                        ~~~~~~~~~~~~~~~~~

src/collection.ts:103:29 - error TS2322: Type 'void | Key' is not assignable to type 'Key | Key[] | undefined'.
  Type 'void' is not assignable to type 'Key | Key[] | undefined'.

103   if (amount === undefined) return this.keys().next().value;
                                ~~~~~~

src/collection.ts:107:52 - error TS2322: Type 'void | Key' is not assignable to type 'Key'.
  'Key' could be instantiated with an arbitrary type which could be unrelated to 'void | Key'.

107   return Array.from({ length: amount }, (): Key => iter.next().value);
                                                       ~~~~~~~~~~~~~~~~~

src/collection.ts:515:10 - error TS2488: Type 'void | [Key, Value]' must have a '[Symbol.iterator]()' method that returns an iterator.

515    const [key, value] = iter.next().value;
             ~~~~~~~~~~~~

src/collection.ts:629:18 - error TS7053: Element implicitly has an 'any' type because expression of type '1' can't be used to index type 'void | [Key, Value]'.
  Property '1' does not exist on type 'void | [Key, Value]'.

629    accumulator = iterator.next().value[1];
                     ~~~~~~~~~~~~~~~~~~~~~~~~


Found 6 errors.

These errors fall into two categories:

• Attempting to access or destructure a value of type T | void.
  • All of these errors occur in places where the length of the iterator has already been checked or derived, so we know that the iterator will never be "done" and will therefore always return a value of type T. It's therefore safe to use ! in these instances.
  • Additionally, under reduce(), if there's no initialValue provided then InitialValue = Value, so it's safe to force the accumulator type (in a similar vein to what already occurs in reduceRight()).
• Attempting to return a value of T | void from a function that returns T | undefined. Although the void value is by definition undefined, this is an assignability error unless coerced.

Status and versioning classification:

• These are changes related to compilation only, and have no effects on the shape or behaviour of the API.
• These changes are fully build-compatible with current versions of TypeScript.