Add GPL-3 notice to all source files

[codergeek42]

Although the current LICENSE inclusion makes clear that this is under the GPL-3.0 "copyleft" license; the preamble should be added to each source file just to be explicitly clear.

Suggested preamble text, from the GPL-3.0 itself with software and author name filled in:

    wordle-solver: A clever algorithm and automated tool to solve the NYTimes daily Wordle puzzle game.
    Copyright (C) 2023 Peter Gordon <codergeek42@gmail.com>

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program, namely the "LICENSE" text file.  If not,
    see <https://www.gnu.org/licenses/gpl-3.0.html>.

Acceptance Criteria This preamble is added a code comment to each source file:

• [x] data/alphabet.ts
• [x] src/lib/nextWordGuesserStrategy.ts
• [x] src/lib/wordleSolver.ts
• [x] src/lib/guesserStrategies/distinctLettersStrategy.ts
• [x] src/lib/guesserStrategies/retryMisplacedLettersStrategy.ts
• [x] src/lib/guesserStrategies/perLetterEliminationStrategy.ts
• [x] src/lib/guesserStrategies/letterFrequencyStrategy.ts
• [x] src/lib/wordleSolverError.ts
• [x] src/lib/helpers/generateAlphabetOfLength.ts
• [x] src/lib/helpers/generateAlphabetWords.ts
• [x] src/lib/letterAtPosition.ts
• [x] src/lib/wordList.ts
• [x] src/lib/wordGuessAndResult.ts
• [x] src/index.ts
• [x] jest.config.js
• [x] eslint.config.mjs
• [x] tests/index.test.ts
• [x] tests/lib/letterAtPosition.test.ts
• [x] tests/lib/wordleSolverError.test.ts
• [x] tests/lib/guesserStrategies/perLetterEliminationStrategy.test.ts
• [x] tests/lib/guesserStrategies/letterFrequencyStrategy.test.ts
• [x] tests/lib/guesserStrategies/retryMisplacedLetterStrategy.test.ts
• [x] tests/lib/guesserStrategies/distinctLetterStrategy.test.ts
• [x] tests/lib/nextWordGuesserStrategy.test.ts
• [x] tests/lib/helpers/generateAlphabetOfLength.test.ts
• [x] tests/lib/helpers/generateAlphabetWords.test.ts
• [x] tests/lib/wordleSolver.test.ts
• [x] tests/lib/wordList.test.ts

[codergeek42]

For posterity: File list as checkboxes markdown generated by CLI:

$ cd wordle-solver
$ find .  -iregex '.*\.[cm]?[tj]s$' | sed -e 's!^\./!- [ ] !g'

[codergeek42]

For posterity: Formatted preamble as TS/JS comment:

/*****
 * wordle-solver: A clever algorithm and automated tool to solve the
 *  NYTimes daily Wordle puzzle game.
 * Copyright (C) 2023 Peter Gordon <codergeek42@gmail.com>
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program, namely the "LICENSE" text file.  If not,
 * see <https://www.gnu.org/licenses/gpl-3.0.html>.
 *****/