Fix statistical seed bias, off-by-one range errors, and resource handling bugs

[Copilot]

Several correctness and robustness bugs affected the quality of generated numbers and the valid parameter space. The most critical issue caused the RNG to be seeded with only 1 byte despite reading 256 bytes of entropy.

Statistical correctness

• Seed entropy truncated: mpz_import(seed, 1, 1, 1, ...) imported only the first byte of the 256-byte entropy buffer. Fixed to mpz_import(seed, count, 1, sizeof(char), ...).
• range was exclusive: Global range was computed as high − low throughout, but the inclusive count high − low + 1 is required for correct uniform sampling and inverse-method sizing. Now set once (correctly) in parse_options().

Off-by-one bugs

• Upper bound excluded from output: The inverse-method scan loop while (mpz_cmp(tmp, high)) never printed high. Fixed to <= 0.
• Range validity check too strict: mpz_cmp(arg_count, range) >= 0 rejected valid counts up to the full range size. Fixed to > 0 (after correcting range to be inclusive).
• invsize undercounted by 1: Was computed from the off-by-one range, causing one fewer exclusion to be generated than needed.

Resource handling

• Wrong buffer size: malloc(count * sizeof(char*) + 1) allocated 8× the needed bytes on 64-bit. Fixed to malloc(count + 1).
• Incomplete read() not retried: A single read() from /dev/random may return fewer bytes than requested. Added a retry loop with error and EOF checks.
• Missing open() and malloc() error checks in init_random().
• Missing null check for malloc in the inverse path of generate_series(); handles invsize == 0 (full-range generation) safely.
• mpz_clear(range) called before mpz_init(range) when exiting via -h/-v/--usage. Fixed by moving mpz_init(range) to main().
• Memory leak in verbose mode: strings from mpz_get_str(NULL, ...) were never freed.

Minor

• Added break after case 'r' (implicit fallthrough to case '?' was harmless but misleading).
• Removed unused high parameter from random_integer() since the global range now holds the inclusive count.
• Suppressed -Wunused-parameter for depth in treeaction() with (void)depth.

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