ra: add support for direct array access notation

[niedbalski]

Description

This PR fixes an issue where the Record Accessor API couldn't handle direct array access patterns like $array[0].

The fix changes the condition that checks if a lookup succeeded by replacing !found with matched == 0, which properly tracks array element access.

Added test cases to verify array access works:

• Direct array access ($array[0])
• Nested array access ($matrix[1][2])
• Mixed array and map access ($records[1]['name'])
• Handling of edge cases (out-of-bounds indices, nonexistent keys, type mismatches)

Fixes #9958

Testing

• Example configuration file for the change

pipeline:
  inputs:
    - name: dummy
      dummy: '{"array": ["a", "b", "c"]}'
  outputs:
    - name: stdout
      match: "*"
      processors:
        logs:
          - name: calyptia
            actions:
              - type: put
                opts:
                  key: "worked"
                  value: "true"
                condition:
                  operator: AND
                  rules:
                    - field: "$array[1]"
                      operator: eq
                      value: "b"

• Debug log output from testing the change

[2025/02/25 14:55:32] [ info] [processor:calyptia:logs.0] added record accessor rule "$array[1]" eq "b"
[2025/02/25 14:55:32] [ info] [processor:calyptia:logs.0] rule condition result: true
[2025/02/25 14:55:32] [ info] [output:stdout:stdout.0] {"array":["a","b","c"],"worked":"true"}

• Attached Valgrind output that shows no leaks or memory corruption was found
  [N/A]

• Run local packaging test showing all targets build
  [N/A]

Documentation

• Documentation required for this feature
  [N/A]

Backporting

• Backport to latest stable release.
  [N/A]

[pwhelan]

LGTM

Must applaud the rigorous testing. Good work!

[edsiper]

in this case, what will happen if the accessed value is another array ?

[niedbalski]

Good question. When the accessed value is another array, the function will process it in the next iteration through if (entry->type == FLB_RA_KEY_ARRAY), which runs before the map type check. This is validated in cb_nested_array_access() test, which successfully accesses $matrix[1][2] from {"matrix": [[1, 2, 3], [4, 5, 6], [7, 8, 9]]} to get the value 6.

[niedbalski]

@edsiper @cosmo0920 I added a few extra test cases to cover cfl conversion as well. PTAL