Add itertools-ts to Functional programming section

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Checklist:

• I've read and understood Contributing Guidelines.
• I've added the new resource at the end of its section.
• This resource is out there for a while, and actively maintained.
• This resource is popular enough and has at least a few hundred stars on GitHub.

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Extended itertools port for TypeScript and JavaScript. Provides a huge set of functions for working with iterable collections (including async ones).

Loop Iteration Tools Example

import { multi } from 'itertools-ts';

for (const [letter, number] of multi.zip(['a', 'b'], [1, 2])) {
  console.log(`${letter}${number}`);  // a1, b2
}

// Async example
for await (const [letter, number] of multi.zipAsync(['a', 'b'].map((x) => Promise.resolve(x)), [1, 2].map((x) => Promise.resolve(x)))) {
  console.log(`${letter}${number}`);  // a1, b2
}

Stream Iteration Tools Example

import { Stream, AsyncStream } from 'itertools-ts';

const result1 = Stream.of([1, 1, 2, 2, 3, 4, 5])
  .distinct()             // [1, 2, 3, 4, 5]
  .map((x) => x**2)       // [1, 4, 9, 16, 25]
  .filter((x) => x < 10)  // [1, 4, 9]
  .toSum();               // 14

// Async example
const result2 = await AsyncStream.of([1, 1, 2, 2, 3, 4, 5].map((x) => Promise.resolve(x)))
  .distinct()             // [1, 2, 3, 4, 5]
  .map((x) => x**2)       // [1, 4, 9, 16, 25]
  .filter((x) => x < 10)  // [1, 4, 9]
  .toSum();               // 14

All functions work on iterable collections and iterators:

• Array
• Set
• Map
• String
• Generator
• Iterable
• Iterator

Every function have an analog with "Async"-suffixed name for working with async iterable and iterators (e.g. zip and zipAsync):

• AsyncIterable
• AsyncIterator

If an asynchronous function takes other functions as input, they can also be asynchronous.

Stream and Async Stream

Streams provide a fluent interface to transform arrays and iterables (sync or async) through a pipeline of operations.

Streams are made up of:

1. One stream source factory method to create the stream.
2. Zero or more stream operators that transform the stream to a new stream.
3. Terminal operation of either:
   • Stream terminal operation to transform the stream to a value or data structure.

     const result1 = Stream.of([1, 1, 2, 2, 3, 4, 5])
       .distinct()             // [1, 2, 3, 4, 5]
       .map((x) => x**2)       // [1, 4, 9, 16, 25]
       .filter((x) => x < 10)  // [1, 4, 9]
       .toSum();               // 14
     
     // Async example
     const result2 = await AsyncStream.of([1, 1, 2, 2, 3, 4, 5].map((x) => Promise.resolve(x)))
       .distinct()             // [1, 2, 3, 4, 5]
       .map((x) => x**2)       // [1, 4, 9, 16, 25]
       .filter((x) => x < 10)  // [1, 4, 9]
       .toSum();               // 14

   • The stream is iterated via a for loop.

     const result1 = Stream.of([1, 1, 2, 2, 3, 4, 5])
       .distinct()             // [1, 2, 3, 4, 5]
       .map((x) => x**2)       // [1, 4, 9, 16, 25]
       .filter((x) => x < 10); // [1, 4, 9]
     
     for (const item of result1) {
       // 1, 4, 9
     }
     
     // Async example
     const result2 = AsyncStream.of([1, 1, 2, 2, 3, 4, 5].map((x) => Promise.resolve(x)))
       .distinct()             // [1, 2, 3, 4, 5]
       .map((x) => x**2)       // [1, 4, 9, 16, 25]
       .filter((x) => x < 10); // [1, 4, 9]
     
     for await (const item of result2) {
       // 1, 4, 9
     }

Full documentation in project's README.