Fix missing algorithm include in null mask

[Moisan]

I spotted in Homebrew/homebrew-core#301351 that ladybug fails to build in some situations. Homebrew CI shows

2026-08-29T20:28:25.4356720Z ##[error]In file included from /private/tmp/ladybug-20260829-4391-uknlsk/ladybug-0.20.0/src/include/binder/bound_scan_source.h:5:
In file included from /private/tmp/ladybug-20260829-4391-uknlsk/ladybug-0.20.0/src/include/binder/bound_table_scan_info.h:4:
In file included from /private/tmp/ladybug-20260829-4391-uknlsk/ladybug-0.20.0/src/include/function/table/table_function.h:5:
In file included from /private/tmp/ladybug-20260829-4391-uknlsk/ladybug-0.20.0/src/include/common/data_chunk/data_chunk.h:8:
In file included from /private/tmp/ladybug-20260829-4391-uknlsk/ladybug-0.20.0/src/include/common/vector/value_vector.h:10:
/private/tmp/ladybug-20260829-4391-uknlsk/ladybug-0.20.0/src/include/common/null_mask.h:85:14: error: no member named 'fill' in namespace 'std'
   85 |         std::fill(data.begin(), data.end(), NO_NULL_ENTRY);
      |              ^~~~
/private/tmp/ladybug-20260829-4391-uknlsk/ladybug-0.20.0/src/include/common/null_mask.h:96:14: error: no member named 'fill' in namespace 'std'
   96 |         std::fill(data.begin(), data.end(), NO_NULL_ENTRY);
      |              ^~~~
/private/tmp/ladybug-20260829-4391-uknlsk/ladybug-0.20.0/src/include/common/null_mask.h:100:14: error: no member named 'fill' in namespace 'std'
  100 |         std::fill(data.begin(), data.end(), ALL_NULL_ENTRY);
      |              ^~~~

null_mask.h uses std::fill in inline methods but did not include <algorithm>, which declares it.

I believe the project previously built only because another included standard header happened to expose std::fill transitively with some compiler/standard-library versions.

This PR adds the direct <algorithm> include so the header is self-contained and portable.