Fix #73: add forced info log level

[mishankov]

Closes #73

Summary

• add log.LevelInfoForced as an exported wide-event level that is always retained by DefaultSampler
• normalize forced-info output so both event records and handler output still render INFO instead of INFO+1
• apply the new level to WideEventLogger.Info(...) when it is used as the package default logger, so explicit info logs are retained after #74
• add focused tests for sampler behavior, event step serialization, wide-event logger output, and base log.New(...) output
• document how to use LevelInfoForced for explicit event retention

Testing

• go test ./log/...
• task test
• task lint

Code Review

• Reviewed the branch diff for correctness/regression risks in sampler behavior, level rendering, and the new default-logger path
• No blocker findings were identified

Notes

• Branch was rebased onto the current origin/main before push so it includes the merged #74 wide-event default logger changes