[Repo Assist] fix: prevent int overflow (UB) in l_strtod/l_strtof exponent parsing

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🤖 This is an automated pull request from Repo Assist.

Summary

Fixes signed-integer overflow (undefined behaviour) in l_strtod and l_strtof when parsing exponent strings with 10 or more digits (e.g., "1e999999999999999").

Root Cause

Both parsers accumulate the exponent into a plain int:

int exp = 0;
while (*s >= '0' && *s <= '9')
    exp = exp * 10 + (*s++ - '0');
if (exp > 308) exp = 308;

For a 10+ digit exponent string such as "1e99999999999", exp overflows int (signed-integer overflow = UB in C). An optimising compiler can miscompile this code by assuming the overflow never occurs.

Fix

Cap accumulation before the multiplication can overflow:

while (*s >= '0' && *s <= '9') {
    if (exp < 10000) exp = exp * 10 + (*s - '0');
    s++;
}

Same fix applied to l_strtof.

Tests

Regression tests added to tests/test_strings.c for both functions covering very-long exponent strings.

Test Status

✅ ./Taskfile test — all non-infrastructure tests pass.

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