build.zig: declare lambda_module as const

[Cloudef]

Zig 0.12 (0.12.0-dev.1664+8ca4a5240) throws error for var declarations that are never mutated.

[softprops]

Thanks for the pull @Cloudef.

I see some changes in here that were compatible with the current stable version 0.11 and some that weren't. Can you limit the changes to changes that will also be 0.11 compatible? When 0.12 is the new stable version of zig I'm happen to accept all of these I don't think there's an eta on when 0.12 will be available and I don't want to focus nightly dependency on users.

[Cloudef]

You can do whatever you want with this PR. I'll probably write my own lambda runtime at some point as I have some special needs. But your project has been great start so far. I think the cleanup callbacks aren't optimal. Better approach may be to let user have a some sort of response object that they can use to write the response, that way it can be done without allocations too.

[softprops]

cool thanks. I've updated the main branch reducing use of needless vars. I'm going to keep this pull open as a reference for updates from 0.11.0 version of std.http.Client to what 0.12.0 will become with that lands.