Use accurate estimate for campaign variables character count

[ajohn25]

Describe the bug
When estimating segment counts, the estimated length of a campaign variable can vary significantly from the actual length

To Reproduce
Steps to reproduce the behavior:

1. Add a campaign variable that has a value with a long link (ex. https://github.com/With-the-Ranks/Spoke) to a campaign
2. Use the campaign variable in a script
3. See that the estimated chracter count for the campaign variable in the segment counter is much lower than we'd expect

Expected behavior
Use the value of the campaign variable (if filled in) to estimate the character count