Harden Distances input and output handling

[krotname]

Motivation

• Prevent local file-clobbering via fixed output.txt and unbounded array allocation from attacker-controlled input by removing fixed-path file I/O and validating sizes.
• Preserve existing algorithm behavior and contest-style entrypoint while removing unsafe defaults that follow symlinks and allow NegativeArraySizeException/OutOfMemoryError.

Description

• Replaced fixed new FileInputStream("input.txt") / new FileOutputStream("output.txt") usage by adding run(InputStream, OutputStream) and delegating the no-arg run() to run(System.in, System.out) so callers supply streams.
• Added private static final int MAX_INPUT_SIZE = 100_000 and validate n with if (n < 1 || n > MAX_INPUT_SIZE) to reject negative, zero, or excessive sizes before allocating the int[].
• Ensured buffered output is fully propagated by calling the underlying stream's flush() from FastOut.flush().
• Added focused tests: src/test/java/algorithms/sprint1/DistancesTest.java for normal stream I/O and invalid sizes, and updated AlgorithmCliTest to exercise Distances.run via standard I/O instead of contest files.

Testing

• Ran git diff --check with no reported whitespace problems.
• Executed mvn -q -Dtest=algorithms.sprint1.DistancesTest test, which passed the new unit tests.
• Executed mvn -q verify, and the full test suite completed successfully (integration and unit tests passed; Maven emitted only a non-failing JDK/deprecation warning).

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Codex Task

[krotname]

Superseded by the validated combined merge in #115: #115