testing/ostest: add strto base tests

[Zepp-Hanzj]

Summary

Add regression coverage to ostest for the explicit-base handling fixed by apache/nuttx#19594.

The new test:

• exhaustively checks bases 2 through 36 with lower- and upper-case digits
• verifies positional values and end pointers
• exercises strtol(), strtoul(), strtoll(), strtoull(), strtoimax(), and strtoumax()
• verifies that bases 1 and 37 still fail with EINVAL
• is included by both the Make and CMake builds

Impact

This only extends ostest; application behavior is unchanged.

Testing

Built sim:ostest with GNU Make against apache/nuttx#19594.

Without the libc fix, the new regression test fails at the first base-27 assertion:

user_main: libc tests
dump_assert_info: Assertion failed : at file: libc_strto.c:58 task: ostest process: ostest
ostest_main: Exiting with status 256

With the libc fix, the libc test section completes and ostest proceeds to the following tests:

user_main: libc tests

End of test memory usage:
...
user_main: setvbuf test

Commit-level style checks also pass:

$ tools/checkpatch.sh -g HEAD~1..HEAD
✔️ All checks pass.

[acassis]

@Zepp-Hanzj seems like there is an issue in our CI:

  Building NuttX...
aarch64-none-elf-ld: /github/workspace/sources/nuttx/nuttx section `.rodata' will not fit in region `ocram'
aarch64-none-elf-ld: section .data LMA [00000000204e0000,00000000204e213f] overlaps section .rodata LMA [00000000204c7000,00000000204e0267]
aarch64-none-elf-ld: region `ocram' overflowed by 616 bytes
make[1]: *** [Makefile:194: nuttx] Error 1
make: *** [tools/Unix.mk:569: nuttx] Error 2
make: Target 'all' not remade because of errors.
/github/workspace/sources/nuttx/tools/testbuild.sh: line 397: /github/workspace/sources/nuttx/../nuttx/nuttx.manifest: No such file or directory
  [1/1] Normalize imx93-evk/bootloader
/github/workspace/sources/nuttx /github/workspace/sources/nuttx
On branch master
Your branch is up to date with 'origin/master'.

@eenurkka could you please take a look, this imx93-evk:bootloader was created by you