fix(git): correct field misalignment in date-filtered git_log

[itguruhaseeb]

Problem

git_log's date-filtered branch parses git log output into fixed groups of 4 lines (hash, author, date, subject), but the pretty-format string ends with a trailing %n:

args.extend(['--format=%H%n%an%n%ad%n%s%n'])

That trailing %n makes git emit a blank line after every commit, so each record occupies 5 slots after .split('\n') while the loop advances by 4. Only the first commit lands on a correct boundary. Every commit after it is shifted by one field, and a commit can be dropped or a spurious blank entry emitted.

Concretely, for a repo with an "initial commit" plus a few filtered commits, the second entry comes back as:

Commit: <author name>
Author: <date string>
Date:   initial commit
Message:

The unfiltered branch (iter_commits, used when no start_timestamp/end_timestamp is given) is correct and unaffected, which is why this went unnoticed.

Fix

Drop the trailing %n so each record is exactly 4 lines and the group-of-4 parser stays aligned:

args.extend(['--format=%H%n%an%n%ad%n%s'])

%s is the commit subject (first line only), so every field is guaranteed single-line and the 4-line grouping is safe.

Test

Adds test_git_log_with_timestamp_filter, which filters by start_timestamp and asserts every commit's fields map correctly across multiple commits. It fails on the old format (returns 5 entries with shifted fields) and passes with the fix. Full git-server suite: 44 passed.