Migrate testStrataCommand.sh from the Strata repo

[atomb]

This tests the strata command beyond running it to verify several examples.

CLI error handling and help output:

• Proper error messages when no args, unknown commands, unknown flags, missing flag values, missing positional args, or extra positional args are passed
• That error messages include per-command hints (e.g. strata check --help, strata diff --help)
• Global --help output shows the expected description
• Per-command --help works, including when mixed with other flags

Ion round-trip correctness:

• Converts a dialect file (Arith) to Ion format via strata toIon
• Pretty-prints the same dialect file via strata print
• Prints the Ion file back and verifies it matches the pretty-printed original (byte-for-byte via cmp)

pyResolveOverloads error handling:

• Verifies the command errors gracefully when given a nonexistent dispatch file

The script uses two helpers (expect_error and expect_output) that check for expected exit codes and substring matches in the output, tracking failures via a failed flag and exiting non-zero if anything fails.

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