Improve router performance with dedicated child types

[pafuent]

Before this commit, all the node types were added to the same list of children nodes. Taking in consideration that only one Param and Any type of node could exist per node, two new node struct field were added to hold the references to those kind of nodes.
This avoid the need to iterate through all the Static type nodes just to find one Param or Any type node. Those iterations could be performed multiple times in the same iteration of Router#Find.
Removing the route comments of the Router benchmark tests.
Updating the Router benchmarks tests to find the routes defined to each particular benchmark. Before, all the benchmarks tried to find only the GitHub API.
Adding new router benchmarks to measure when the Router try to find routes that are not registered.

To be fair in the below benchmarks, I did the same modifications to the Router benchmarks on master. Also I performed 10 iterations per each benchmark, and compared the results with benchstat

benchstat bench_master.txt bench_new.txt

name                         old time/op    new time/op    delta
RouterStaticRoutes-2           20.0µs ± 2%    20.3µs ± 5%     ~     (p=0.065 n=10+9)
RouterStaticRoutesMisses-2     1.02µs ± 2%    0.66µs ± 4%  -35.43%  (p=0.000 n=8+9)
RouterGitHubAPI-2              38.9µs ± 3%    37.0µs ± 4%   -4.77%  (p=0.000 n=10+10)
RouterGitHubAPIMisses-2        1.25µs ± 3%    0.77µs ± 6%  -38.39%  (p=0.000 n=10+10)
RouterParseAPI-2               2.08µs ±10%    1.98µs ± 3%   -4.71%  (p=0.029 n=10+10)
RouterParseAPIMisses-2          442ns ± 4%     452ns ± 3%     ~     (p=0.066 n=9+9)
RouterGooglePlusAPI-2          1.35µs ± 2%    1.29µs ± 3%   -4.27%  (p=0.000 n=10+10)
RouterGooglePlusAPIMisses-2     989ns ± 4%     662ns ± 8%  -33.06%  (p=0.000 n=10+10)
RouterParamsAndAnyAPI-2        3.34µs ± 1%    2.96µs ± 3%  -11.41%  (p=0.000 n=8+10)

name                         old alloc/op   new alloc/op   delta
RouterStaticRoutes-2            0.00B          0.00B          ~     (all equal)
RouterStaticRoutesMisses-2      0.00B          0.00B          ~     (all equal)
RouterGitHubAPI-2               0.00B          0.00B          ~     (all equal)
RouterGitHubAPIMisses-2         0.00B          0.00B          ~     (all equal)
RouterParseAPI-2                0.00B          0.00B          ~     (all equal)
RouterParseAPIMisses-2          0.00B          0.00B          ~     (all equal)
RouterGooglePlusAPI-2           0.00B          0.00B          ~     (all equal)
RouterGooglePlusAPIMisses-2     0.00B          0.00B          ~     (all equal)
RouterParamsAndAnyAPI-2         0.00B          0.00B          ~     (all equal)

name                         old allocs/op  new allocs/op  delta
RouterStaticRoutes-2             0.00           0.00          ~     (all equal)
RouterStaticRoutesMisses-2       0.00           0.00          ~     (all equal)
RouterGitHubAPI-2                0.00           0.00          ~     (all equal)
RouterGitHubAPIMisses-2          0.00           0.00          ~     (all equal)
RouterParseAPI-2                 0.00           0.00          ~     (all equal)
RouterParseAPIMisses-2           0.00           0.00          ~     (all equal)
RouterGooglePlusAPI-2            0.00           0.00          ~     (all equal)
RouterGooglePlusAPIMisses-2      0.00           0.00          ~     (all equal)
RouterParamsAndAnyAPI-2          0.00           0.00          ~     (all equal)

[codecov]

Codecov Report

Merging #1689 (045bec5) into master (4422e3b) will increase coverage by 0.11%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1689      +/-   ##
==========================================
+ Coverage   85.19%   85.30%   +0.11%     
==========================================
  Files          29       29              
  Lines        1986     2001      +15     
==========================================
+ Hits         1692     1707      +15     
  Misses        186      186              
  Partials      108      108              

Impacted Files	Coverage Δ
router.go	97.05% <100.00%> (+0.17%)	⬆️

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[lammel]

@pafuent I do not see too much risk in changed behaviour as our router tests are pretty helpful here.
So I'm in favour of merging. Patch looks good based on the code, haven't tried the branch yet.

I'm missing our github action for benchmark comparison though.

[pafuent]

Sadly the GitHub action won't be fair in this case, because I changed the benchmarks on this PR. In this case you will need to trust on my benchmarks 😉

[lammel]

Please rebase to master.

[pafuent]

@lammel rebased