feat: add deterministic seeding support

Per-call local engine architecture mirroring entity-generator:
- get_nickname(name, seed) overload for reproducible generation
- seed()/unseed() for deterministic sequences (thread-local)
- nickname::seed() accessor for replay

Changed all 28 transform functions to accept effolkronium::random_local&
instead of using the global random_thread_local. Each get_nickname() call
draws a seed from the thread-local engine, creates a stack-local engine,
and threads it through solver → leetify → format → transforms.

Thread safety preserved: seed drawing uses thread_local storage,
generation uses stack-local engine. Concurrent get_nickname() remains safe.

8 new seeding tests.
Updated example with deterministic generation demo.
Updated copyright to 2020-2026.

Author: dasmig

LICENSE.MIT

@@ -1,6 +1,6 @@
 MIT License 
 
-Copyright (c) 2020-2022 Diego Dasso Migotto
+Copyright (c) 2020-2026 Diego Dasso Migotto
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

README.md

@@ -21,7 +21,7 @@ The library currently supports the following:
 
 - **Nickname Generation**. The library randomly generates a nickname based on either a name or a list of words.
 
-- **'Leetifying' Process**. After selecting a name/word it will randomly apply any number of customizations to uniquefy the nickname.
+- **Leetifying Process**. After selecting a name/word it will randomly apply any number of customizations to uniquefy the nickname.
 
 - **Word Lists Supported**. Currently the following word lists are supported and a matching database is packed together with the library:
   - Adjectives