Fix truncation marker overflow

[hiSandog]

Summary:

• Keep truncateStringWithMessage outputs within maxLength when the truncation marker is longer than the limit.
• Cover END, START, and MIDDLE truncation edge cases.
• Preserve context around the marker when the limit is large enough.

Validation:

• /Users/sandog/.real/.bin/bun test common/src/util/tests/string.test.ts
• git diff --check