fix: Migrate away from lazy_static in favor of thread_local

The new secret memory pool was causing CI failures in the fuzzing code,
due to the fuzzer compiling its binaries with memory sanitizer support.

https://doc.rust-lang.org/beta/unstable-book/compiler-flags/sanitizer.html

Using lazy_static was – intentionally – introducing a memory leak, but the
LeakSanitizer detected this and raised an error.

Now by using thread_local we are calling the destructors and so – while still being a
memory leak in practice – the LeakSanitizer no longer detects this behaviour as an error.

Alternatively we could have used a known-leaks list with the leak-sanitizer, but this would have increased the complexity of the build setup.

Finally, this was likely triggered with the migration to memsec, because libsodium circumvents the malloc/free calls,
relying on direct calls to MMAP.

Cargo.toml

@@ -42,7 +42,6 @@ doc-comment = "0.3.3"
 base64 = "0.21.5"
 zeroize = "1.7.0"
 memoffset = "0.9.0"
-lazy_static = "1.4.0"
 thiserror = "1.0.50"
 paste = "1.0.14"
 env_logger = "0.10.1"