[LEMS-2772] enable strict-boolean-expressions rule and add file ignores

[tatianasnook]

• Added @typescript-eslint/strict-boolean-expressions rule to enforce explicit boolean expressions.
• Configured @typescript-eslint/parser and parserOptions in .eslintrc.js to support type-aware linting.
• Updated .eslintignore to exclude config, test, and non-source files.
• Updated tsconfig.json to exclude files not part of the main source.
• Temporarily disabled strict-boolean-expressions errors using inline and file-level eslint-disable comments.

[github-actions]

Size Change: -2.98 kB (-0.34%)

Total Size: 873 kB

Filename	Size	Change
packages/kas/dist/es/index.js	39.7 kB	+71 B (+0.18%)
packages/kmath/dist/es/index.js	11.2 kB	+31 B (+0.28%)
packages/math-input/dist/es/index.js	77.7 kB	+137 B (+0.18%)
packages/perseus-core/dist/es/index.js	32 kB	+133 B (+0.42%)
packages/perseus-editor/dist/es/index.js	275 kB	-943 B (-0.34%)
packages/perseus-linter/dist/es/index.js	20 kB	-2.83 kB (-12.42%)	👏
packages/perseus-score/dist/es/index.js	20.7 kB	+88 B (+0.43%)
packages/perseus/dist/es/index.js	370 kB	+115 B (+0.03%)
packages/perseus/dist/es/strings.js	6.78 kB	+49 B (+0.73%)
packages/pure-markdown/dist/es/index.js	4.18 kB	+37 B (+0.89%)
packages/simple-markdown/dist/es/index.js	13.2 kB	+128 B (+0.98%)

ℹ️ View Unchanged

Filename	Size
packages/keypad-context/dist/es/index.js	760 B
packages/math-input/dist/es/strings.js	1.79 kB

_{compressed-size-action}

[github-actions]

npm Snapshot: Published

Good news!! We've packaged up the latest commit from this PR (4eeef33) and published it to npm. You
can install it using the tag PR2302.

Example:

pnpm add @khanacademy/perseus@PR2302

If you are working in Khan Academy's webapp, you can run:

./dev/tools/bump_perseus_version.sh -t PR2302