rename project to MultiforaDB

Prose and benchmark tables use MultiforaDB; the binary, the CLI usage
line, the log-message prefix and the default database file use
multiforadb.

Two consequences worth noting:

- build.zig.zon's fingerprint is derived from the package name, so it
  had to change with it (Zig refuses to build otherwise). A consumer
  pinning this package by fingerprint needs updating.
- the default --db path is now multiforadb.log, and getCmdLineOpts
  reports it as dbpath. An existing mongo-lite.log has to be passed
  explicitly with --db.

The e2e harness abbreviated the old name as ML_; that is now MFDB_,
including the documented ML_BIN override (MFDB_BIN) and the scratch
file names. MD_ (mongod) is untouched.

compare-run.sh spawned the server by absolute path under a
sandbox/mongo-lite directory that no longer exists; that block already
runs from tests/e2e, so it uses a relative path now.

The archived reports under tests/e2e/results/ keep the old name: they
record what the old binary measured.

tests/e2e/concurrent.js

@@ -2,7 +2,7 @@
 // insertOne ({w:1, j:true} by default) into their own collection, reporting
 // aggregate docs/s. Exercises the group-commit path under real contention.
 //
-//   node tests/e2e/concurrent.js --url mongodb://127.0.0.1:27019 --label mongo-lite
+//   node tests/e2e/concurrent.js --url mongodb://127.0.0.1:27019 --label multiforadb
 //                                 [--clients 8] [--per-client 2000] [--wc j|none]
 //
 // Output (stdout, tab-separated, one line):