Normalize decimal integer and exit-code validation

[codeforester]

Problem

Several stdlib numeric contracts accept decimal-looking strings but pass them directly to Bash arithmetic, where a leading zero selects octal interpretation.

At main commit a107134:

• n=08; assert_integer_range n 0 10 prints an arithmetic error and then returns success.
• exit_if_error 08 message prints an arithmetic error and continues instead of exiting.
• assert_arg_count 08 0 10 can also continue after an arithmetic error.
• assert_integer_range value 10 1 treats an inverted range as an ordinary out-of-range value instead of invalid helper usage.

Validation helpers must never turn malformed arithmetic into a successful guard.

Scope

• Normalize accepted integer strings to base-10 before arithmetic, including signs and leading zeros.
• Validate that range minimum is not greater than maximum.
• Require argument counts and bounds to be non-negative where the API represents counts.
• Validate exit_if_error statuses as decimal shell exit codes and define handling outside 0..255.

Acceptance Criteria

• 08, 09, +08, and -08 are handled as decimal values where signed integers are accepted.
• No accepted numeric input emits a Bash arithmetic syntax error.
• Invalid ranges and exit codes fail through library diagnostics rather than continuing.
• Existing valid integer and status behavior remains unchanged.

Validation

• bats lib/bash/std/tests/lib_std.bats
• ./tests/validate.sh
• git diff --check

[codeforester]

Implemented by merged PR #172. Decimal values are normalized before arithmetic, inverted ranges are rejected, and exit/status validation fails explicitly. The leading-zero and inverted-range regressions are covered in lib/bash/std/tests/lib_std.bats.