This commit revises the locking strategy for `partialCached`. We have added a benchmark that may be a little artificial, but it should at least show that we're not losing any performance over this:
```bash
name old time/op new time/op delta
IncludeCached-10 12.2ms ± 2% 11.3ms ± 1% -7.36% (p=0.029 n=4+4)
name old alloc/op new alloc/op delta
IncludeCached-10 7.17MB ± 0% 5.09MB ± 0% -29.00% (p=0.029 n=4+4)
name old allocs/op new allocs/op delta
IncludeCached-10 128k ± 1% 70k ± 0% -45.42% (p=0.029 n=4+4)
```
This commit also revises the template metrics hints logic a little, and add a test for it, which output is currently this:
```bash
cumulative average maximum cache percent cached total
duration duration duration potential cached count count template
---------- -------- -------- --------- ------- ------ ----- --------
163.334µs 163.334µs 163.334µs 0 0 0 1 index.html
23.749µs 5.937µs 19.916µs 25 50 2 4 partials/dynamic1.html
9.625µs 4.812µs 6.75µs 100 50 1 2 partials/static1.html
7.625µs 7.625µs 7.625µs 100 0 0 1 partials/static2.html
```
Some notes:
* The duration now includes the cached invocations (which should be very short)
* A cached template gets executed once before it gets cached, so the "percent cached" will never be 100.
Fixes#4086Fixes#9506
In the internal Radix we stored the directory based nodes without a traling slash, e.g. `/blog`.
The original motivation was probably to make it easy to do prefix searching: Give me all ancestors.
This, however have lead to some ambigouty with overlapping directory names.
This particular problem was, however, not possible to work around in an easy way, so from now we store these as `/blog/`.
Fixes#7301
