R1:dad17fb98a6b

Make "metamta.differential.inline-patches" imply a reasonable byte limit, not just a line limit

Summary:
Fixes T11748. This option currently implies a line limit (e.g., inline patches that are less than 100 lines long). This breaks down if a diff has a 10MB line, like a huge blob of JSON all on one line.

For now, imply a reasonable byte limit (256 bytes per line).

See T11767 for future work to make this and related options more cohesive.

Test Plan:
- With option at `1000`: sent Differential email…