context: #1103

This necessitated a new sentinel value for handling very large (64-bit) ulong, as we need to encode/decode them differently (obviously, they're not large negative numbers) - but we treat everything up to 63-bit as the previous long, for simplicity.

Adding these operators made some of the other operators ambiguous (from the compiler's perspective), so additional operators were also added to make this work without complaint.

Additionally:

• some tweaks to remove unnecessary string allocations (by using the Utf8Parser) were exploited
• all existing direct access to the overloaded field were removed; that was getting dangerous - there are now properties for all of these uses