A param option's value is bounded by length where a magnitude is meant

[xroche]

optalias_param_takes() (#1427) bounded a param row's value at 16 characters, which is a length where a magnitude is meant. It refused --depth=0000000000000000001 for its padding alone, and accepted --sockets=1234567890123456, sixteen digits that sscanf("%d") then read as 1015724736 simultaneous connections. Each digit run is now converted with strtoll and range-checked against what the option's own parser holds: INT_MAX for the rows reading an int, INT64_MAX for -m, -M and -G on their LLint and for -%c, whose float takes any run strtoll converts. The check runs per operand, so the second half of -m N,N2 and -%c 0.5 is covered too. optalias_suffix() carried a copy of the same bare 16, so the six level rows get the same treatment.

The behaviour change is the fix rather than a side effect of it, and it goes both ways. Refused from now on: a value on an int-valued long form whose digit run exceeds 2147483647 and which the old cap let through, so no longer than 16 characters. --sockets=1234567890123456, --max-rate=3000000000, --depth=2147483648, --timeout=99999999999, --generate-errors=3000000000, and every value of that shape on the other int rows. All of them were undefined at sscanf("%d") and wrapped in practice: 1015724736 sockets, a rate of -1294967296, a depth of -2147483648, a timeout of 1215752191 seconds. None landed on a sane value by accident either, since -c clamps its wrapped negative back to one socket, which is still not what was asked for.

Accepted from now on: a zero-padded value wherever its magnitude fits, and on -m, -M, -G and -%c any 17-to-19-digit run up to INT64_MAX. --max-size=9223372036854775807 is refused on master and taken here, which is right, because that is what the LLint behind it holds.

The old cap was also the only thing keeping a value short enough to glue into the 1024-byte expansion buffer, where strlcatbuff aborts rather than clips. So a length bound stays, at the glue site and sized to the room the short form leaves: without it httrack --depth $(printf '0%.0s' $(seq 1022)) exits 134 with a backtrace where master printed a syntax error. It now also reaches a class the old cap never covered, the param0 rows, where httrack --allow <1023 chars> aborts on master and draws the same syntax error here.

369 asserts both directions, through the engine's own expansion and on disk, and reds on six mutants: the length cap put back, optalias_run_fits forced true or stripped of its max, the LLint arm narrowed to -M and -%c, a leading sign accepted, the capacity guard removed, and optalias_suffix reverted. st_optalias's table-wide loop carries the padding, INT_MAX and sign probes across all 27 param rows.

Closes #1437