* refact(validators)

Readability improvements:
* Introduced private constructors for all validators
* All private constructors can use a *SchemaValidatorOptions (generalize
  options passing pattern)
* All exported methods use private constructors (hide the implementation
  of options)
* Readability: reduced the level of indentation with early exit
  conditions than nested conditions
* Object validator: refactored Validate in smaller functions
* Removed dead code/commented out code

Minor efficiency improvements

* In Applies method: reflect replaced by type switch whenever possible
* Removed (mostly unusable) debugLog
* In object validator:
  * pattern properties now use the regexp cache readily available
  * split path may be performed only once
* In schema props: keep arrays of pointers []*SchemaValidator and avoid
  copying a new schema
* In default & example validators:
  * map[string]bool -> map[string]struct{}
  * clear, don't reallocate the visited map
* []validator slice -> [n]validator array

* introduced a benchmark follow-up document, based on the existing Kubernetes API
  fixture

Signed-off-by: Frederic BIDON <[email protected]>

* fixed typo

Signed-off-by: Frederic BIDON <[email protected]>

---------

Signed-off-by: Frederic BIDON <[email protected]>

This PR is a follow-up on #169, which cames with innocuous changes, but already
reduced the total number of allocations when validating a swagger spec.

We reduce further the pressure on go's GC by pooling temporarily
allocated objects: validators and results.

When recursively allocating validators, calls to "Validate()" redeem to the pool the allocated
validator. This means that a validator is usable only once.

A similar approach is taken for `Result`s: upon merge, the merged result
is redeemed to the pool.

Eventually, temporarily allocated `spec.Schema`s are also pooled.

In order not to break existing interfaces, this is enabled by default
only when validating a spec (`Spec()`) or when using
`AgainstSchema()`.

Another option at the spec level allows for skipping the gathering of schemas
into the result ("schemata"): these schemas must be cloned to remain
valid after their parent is redeemed to the pool.

Comment on the benchmark:

CPU profiling shows that about 30% of the CPU time is spent managing
garbage.

Memory profiling shows that our benchmark (validating the k8s API spec) goes
down from 25M allocated objects down to ~ 17M (#169 went down from 60M to 25M).

The `Validate` method generates only ~ 5M of those, out of which
~ 4M are caused by the schema unmarshaling & expansion and 1M by string
allocations for the validator "path".
Unfortunately, classic string interning methods don't work well with this dynamic "path",
so I leave it there.

Integration tests (go-swagger/go-swagger#3064)
show a significant improvement when running go-swagger validate in codegen.

* contributes: go-swagger/go-swagger#2649

Further improvements would most likely come from optimizing the
validation of defaults and examples (which amount for 2M allocs).

Signed-off-by: Frederic BIDON <[email protected]>

Signed-off-by: Frédéric BIDON <[email protected]>

Bumps the development-dependencies group with 3 updates: [actions/checkout](https://github.com/actions/checkout), [actions/setup-go](https://github.com/actions/setup-go) and [codecov/codecov-action](https://github.com/codecov/codecov-action).


Updates `actions/checkout` from 3 to 4
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...v4)

Updates `actions/setup-go` from 4 to 5
- [Release notes](https://github.com/actions/setup-go/releases)
- [Commits](actions/setup-go@v4...v5)

Updates `codecov/codecov-action` from 3 to 4
- [Release notes](https://github.com/codecov/codecov-action/releases)
- [Changelog](https://github.com/codecov/codecov-action/blob/main/CHANGELOG.md)
- [Commits](codecov/codecov-action@v3...v4)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: development-dependencies
- dependency-name: actions/setup-go
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: development-dependencies
- dependency-name: codecov/codecov-action
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: development-dependencies
...

Signed-off-by: dependabot[bot] <[email protected]>

Bumps the go-openapi-dependencies group with 2 updates: [github.com/go-openapi/analysis](https://github.com/go-openapi/analysis) and [github.com/go-openapi/swag](https://github.com/go-openapi/swag).


Updates `github.com/go-openapi/analysis` from 0.22.0 to 0.22.2
- [Commits](go-openapi/analysis@v0.22.0...v0.22.2)

Updates `github.com/go-openapi/swag` from 0.22.8 to 0.22.9
- [Commits](go-openapi/swag@v0.22.8...v0.22.9)

---
updated-dependencies:
- dependency-name: github.com/go-openapi/analysis
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: go-openapi-dependencies
- dependency-name: github.com/go-openapi/swag
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: go-openapi-dependencies
...

Signed-off-by: dependabot[bot] <[email protected]>

Signed-off-by: Frédéric BIDON <[email protected]>