Finished(?) decompression stuff

src/decomp/zig/lzma.zig

@@ -0,0 +1,18 @@
+const std = @import("std");
+const lzma = std.compress.lzma;
+const Reader = std.Io.Reader;
+
+const Decompressor = @import("../../decomp.zig");
+
+interface: Decompressor = .{ .vtable = .{ .stateless = stateless } },
+
+pub fn stateless(alloc: std.mem.Allocator, in: []u8, out: []u8) Decompressor.Error!usize {
+    var rdr: Reader = .static(in);
+    var decomp = try lzma.decompress(alloc, rdr.adaptToOldInterface());
+    defer decomp.deinit();
+    const len = decomp.read(out) catch |err| return switch (err) {
+        error.CorruptInput, error.EndOfStream, error.Overflow => Decompressor.Error.ReadFailed,
+        else => err,
+    };
+    return len;
+}