D7: editor multi-cursor support

Add secondary_cursors field to Editor with insert_char_multi,
delete_back_multi, delete_forward_multi methods. Right-to-left
processing ensures position shifts don't corrupt earlier insertions.

7 new tests: add/clear, all_positions, insert, delete_back,
delete_forward, unicode, duplicate-add.

local/recipes/system/evdevd/source/Cargo.toml

@@ -4,8 +4,8 @@ version = "0.2.5"
 edition = "2021"
 
 [dependencies]
-redox-scheme = "0.11"
-syscall = { package = "redox_syscall", version = "0.8" }
+redox-scheme = { path = "../../../../../local/sources/redox-scheme" }
+syscall = { path = "../../../../../local/sources/syscall", package = "redox_syscall" }
 log = { version = "0.4", features = ["std"] }
 thiserror = "2"
 orbclient = { version = "0.3", default-features = false }
@@ -14,3 +14,7 @@ orbclient = { version = "0.3", default-features = false }
 redox_event = "0.4"
 
 [workspace]
+
+[patch.crates-io]
+redox-scheme = { path = "../../../../../local/sources/redox-scheme" }
+redox_syscall = { path = "../../../../../local/sources/syscall" }