Bridge: Replace lazy_static macro with once_cell

[svix-nick]

See also #1024

lazy_static is unmaintained, once_cell is the new hotness. This PR swaps out the one lazy_static invocation for the equivalent lazy construct from once_cell.

[svix-nick]

⭐ Open source review ⭐

Might not be necessary, but given that this is technically a different project, here's what I said last time:

once_cell is the new standard for lazily-initialized static values. The intent is for its API to be incorporated into the standard library. Parts of it already have been as of Rust 1.70.0.

Our existing solution lazy_static is not maintained, and urges users to move to once_cell.

once_cell is dual licensed Apache 2.0 and MIT, as are all of its dependencies.

[svix-onelson]

OSS review approved!