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.

build.zig

@@ -23,7 +23,7 @@ pub fn build(b: *std.Build) void {
     });
 
     const exe = b.addExecutable(.{
-        .name = "mongo-lite",
+        .name = "multiforadb",
         .root_module = exe_mod,
     });
     b.installArtifact(exe);
@@ -31,7 +31,7 @@ pub fn build(b: *std.Build) void {
     const run_cmd = b.addRunArtifact(exe);
     run_cmd.step.dependOn(b.getInstallStep());
     if (b.args) |args| run_cmd.addArgs(args);
-    const run_step = b.step("run", "Run mongo-lite server");
+    const run_step = b.step("run", "Run multiforadb server");
     run_step.dependOn(&run_cmd.step);
 
     const test_mod = b.createModule(.{