Optimize URL Key Generation for Large Counters

[jaiyankargupta]

The toBase62 function might become inefficient with very large counters due to the repeated modulo and division operations. Investigate and implement a more efficient algorithm for converting numbers to a Base62 string.

Steps to Reproduce:

1. Install the extension.
2. Shorten a very large number of URLs to increase the counter.
3. Observe the performance of the key generation process as the counter increases.

Expected Behavior:
The key generation process should remain performant even with very large counter values.