fix: handle compile errors

[matheusfm]

Description

This PR handles compilation errors of validations and variables and implements unit test for Compile function.

How has this been tested?

• Running the unit tests: make test
• Scanning with a custom check with invalid variable or validation:

cat << 'EOF' > tmp/check.yaml
id: test
severity: High
message: "invalid validation"
match:
  resources:
    - group: ""
      version: v1
      resource: pods
validations:
  - expression: allContainers.all(variables.foo)
EOF
go run main.go scan --disable-builtin --checks /tmp/check.yaml 

Now we expect to see an error like this:

E0318 17:03:19.731543   54820 scan.go:218] "msg"="failed to compile check test" "error"="validations[0].expression: type-check error: ERROR: <input>:1:18: undeclared reference to 'all' (in container '')\n | allContainers.all(variables.test)\n | .................^\nERROR: <input>:1:19: undeclared reference to 'variables' (in container '')\n | allContainers.all(variables.test)\n | ..................^" "check"="test"
I0318 17:03:19.731708   54820 scan.go:186] "msg"="scan finished with errors" 
SEVERITY   ID     CHECK                STATUS   FAILED   PASSED   SKIPPED 
High       test   invalid validation   ERROR    0        0        0         
exit status 2

Checklist

• I have labeled this PR with the relevant Type labels
• I have documented my code (if applicable)
• My changes are covered by tests