Make all parsing extensions "double-requirable"

[joelgallant]

Ensure and test that every parsing extension we have can be included twice without issue.

• [ ] $if
• [ ] $try
• [ ] $eq
• [ ] $hidden
• [ ] $override
• [ ] $extends
• [ ] $env
• [ ] $timestamp
• [ ] $envVar
• [ ] $substitute
• [ ] $git
• [ ] enc:
• [ ] v1-compat
• [ ] vault
• [ ] $exec
• [ ] $jsModule

[joelgallant]

We could do this with a named parsing extension util, like the forKey wrapper. ParsedValue can do a unique on name of each.