Reject negative, fractional and out-of-range numbers when encoding

[sc0Vuai]

Numeric::encode silently encoded negative numbers as zero (-1 -> 80), truncated fractional floats (1.5 -> 01), and crashed with a TypeError for floats written in exponent form (1e15, 1e20), INF, NAN and non-numeric strings.

Accept only non-negative integers up to PHP_INT_MAX (including integral floats such as 1024.0 and 1e15) and throw InvalidArgumentException otherwise. Larger values should be passed as hex strings. Remove the unreachable number_format branch.

Replace the testIssue14 assertions that expected -1/-2 to encode as 80 and add valid/invalid numeric vectors.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.29%. Comparing base (1478705) to head (f2c2f17).

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #35      +/-   ##
============================================
+ Coverage     94.44%   95.29%   +0.84%     
- Complexity       61       66       +5     
============================================
  Files             3        3              
  Lines           162      170       +8     
============================================
+ Hits            153      162       +9     
+ Misses            9        8       -1     

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