Follow up to #42321 - [ads] Add SmartNTT numerical condition matcher defaults

[btlechowski]

Description

Default value for explicit matcher fails.

matcher:

                    "conditionMatchers": [{
                            "prefPath": "tab_stats.window_count_maxFAIL",
                            "condition": "0"
                        }
                    ],

Steps to reproduce

1. Clean profile
2. Run Brave
3. Make sure NTT component is downloaded
4. Use matcher:

                   "conditionMatchers": [{
                           "prefPath": "tab_stats.window_count_maxFAIL",
                           "condition": "0"
                       }
                   ],

5. Trigger NTT ad

Actual result

Ad is not served.

Expected result

Ad is served.

Reproduces how often

Easily reproduced

Brave version (brave://version info)

Brave	1.75.32 Chromium: 131.0.6778.69 (Official Build) nightly (64-bit)
Revision	3ef3853f2179ab519d1c7ed5ec64df16d5b6ceb1
OS	Linux

cc @tmancey @aseren @iambrianfung

[tmancey]

@btlechowski the condition matcher is incorrect, it should be [R=]:0 to match against zero.

[tmancey]

@btlechowski @iambrianfung default value for explicit matcher is not supported, as above, and if we added it could make debugging matchers more difficult. Great idea @btlechowski but closing as wont fix for now due to the debugging.