Bug: stats.lua - inconsistent use of anchors in match patterns

The stats.lua script uses string:match() lots of times when processing query parameters.

In most cases the regex is not anchored, which means that the parameter can contain additional characters. This may cause unexpected behaviour, especially if the parameter is matched more than once with different REs.

Read stats.lua and enumerate the string:match calls used for query parameters. Check how each pattern handles the full parameter value, then verify that valid parameters still match while values with additional characters no longer do.

Written by the indexing model from the issue text.