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.

src/assert.zig

@@ -17,14 +17,14 @@ const std = @import("std");
 
 /// Panic unless `ok`. Active in every optimize mode; see the module comment.
 pub fn assert(ok: bool) void {
-    if (!ok) @panic("mongo-lite: assertion failed");
+    if (!ok) @panic("multiforadb: assertion failed");
 }
 
 /// Panic unless `ok`, naming the invariant that broke. Prefer this where the
 /// condition alone does not say what went wrong -- the message lands in the
 /// crash output, which may be all an operator has to go on.
 pub fn assert_msg(ok: bool, comptime message: []const u8) void {
-    if (!ok) @panic("mongo-lite: assertion failed: " ++ message);
+    if (!ok) @panic("multiforadb: assertion failed: " ++ message);
 }
 
 test "assert passes on true and is callable in every mode" {