Add "grep" sub-command to Rust impl as well

[kmoppel]

The main idea compared to good old grepping is that it preserves full log entries - including the full SQL query for example

[gintsgints]

@kmoppel could you please give some good example of log case, where "full SQL query" is preserved.

[kmoppel]

I think any multi-line SQL will do for testing - e.g. one on testdata/debian_default.log. So running pgweasel grep dasda testdata/debian_default.log should return:

2025-05-02 18:25:51.151 EEST [2698052] krl@postgres ERROR:  syntax error at or near "adsdas" at character 23
2025-05-02 18:25:51.151 EEST [2698052] krl@postgres STATEMENT:  select dadasdas
	dasda
	adsdas;

The first entry does not match text but same event by time + pid