implements ScorePlugin

[codefromthecrypt]

What type of PR is this?

/kind feature

What this PR does / why we need it:

This implements ScorePlugin. Notably, this reduces the size of the score returnable by wasm to int32 from int64 for reasons elaborated in the RATIONALE.md.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Thanks a lot to @anuraaga and @ncruces for helping with the wasm aspects of the rationale.

Thanks a lot to @kerthcet and @sanposhiho for helping with the value space aspects of the score plugin.

Does this PR introduce a user-facing change?

Only notable behavior is reducing the value range of score produced by wasm plugins to max int32.

What are the benchmark results of this change?

goos: darwin
goarch: arm64
pkg: sigs.k8s.io/kube-scheduler-wasm-extension/internal/e2e
                                            │   old.txt   │               new.txt               │
                                            │   sec/op    │   sec/op     vs base                │
PluginFilter/noop/params:_small-12            179.5n ± 0%   181.0n ± 0%  +0.84% (p=0.002 n=6)
PluginFilter/noop/params:_real-12             178.8n ± 1%   182.3n ± 1%  +1.96% (p=0.004 n=6)
PluginFilter/filter-simple/params:_small-12   6.750µ ± 2%
PluginFilter/filter-simple/params:_real-12    50.62µ ± 2%
PluginFilter/noop-wat/params:_small-12                      120.1n ± 0%
PluginFilter/noop-wat/params:_real-12                       119.8n ± 0%
PluginFilter/wasm/params:_small-12                          6.671µ ± 1%
PluginFilter/wasm/params:_real-12                           50.26µ ± 2%
PluginScore/noop-wat/params:_small-12                       120.5n ± 2%
PluginScore/noop-wat/params:_real-12                        122.0n ± 1%
PluginScore/noop/params:_small-12                           244.5n ± 4%
PluginScore/noop/params:_real-12                            206.5n ± 1%
PluginScore/wasm/params:_small-12                           5.082µ ± 5%
PluginScore/wasm/params:_real-12                            49.80µ ± 1%
geomean                                       1.820µ        746.4n       +1.39%               ¹
¹ benchmark set differs from baseline; geomeans may not be comparable

[kerthcet]

/hold

[codefromthecrypt]

In theory, yes, we have no idea how people design their plugins. Although after normalizing, they will be in the range of [0, 100]

ok I will put the note in that normalizing means [0, 100] so basically regardless of number above 100 it normalizes to 100.

[codefromthecrypt]

So, next steps for me are:

• make sure the score and status results are signed, even if narrowed to 32-bits. This increases parity even, even if negative values aren't semantically defined for either.
• consolidate confusingly large types mapped to also too large types, but more convenient ones, into a section. It seems a trend to accidentally (int64) or by default (int) use really large types for values never intended to be large).
  • This allows us to refer to that section in places handling type differences.
  • Add to this section that especially in score it is unnecessary as the usable range is [0, 100]
  • Add to this section that the user can only define 2 billion custom positive status codes now ;)
• restructure the notes currently specifically about score into a general note about when returning two values.
• fill some tests.

Will push a commit to include this!

[codefromthecrypt]

ok spent another hour plus on docs. I think that's way over budget for me and unparalleled in practice.

Next is test.

[codefromthecrypt]

ok addressed all the TODO I'm aware of, PTAL!

[codefromthecrypt]

once last feedback is in, I will squash so that the commit history isn't junked up

[codefromthecrypt]

thanks for the looks folks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: anuraaga, codefromthecrypt, kerthcet, sanposhiho

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