Add JavaScript concepts 34–48 to README

[Krishvora22]

This PR adds JavaScript concepts from 34 to 48 to the README.md file, including:

34. Event Delegation
35. Debouncing and Throttling
36. JavaScript Memory Management
37. Web Workers and Multi-threading
38. Proxy and Reflect
39. Hoisting in JavaScript
40. Closures
41. Modules and Import/Export (ES6 Modules)
    42.Template Literals and Tagged Templates
42. Destructuring Assignment
43. Spread and Rest Operators
44. Optional Chaining and Nullish Coalescing
45. Template Literals and String Interpolation
46. Short-Circuit Evaluation (&&, ||, ??)
47. Type Conversion and Coercion

Each topic includes articles, videos, and back-to-top links in the README.