core/filtermaps: optimize memory allocation with bitset and cache reuse

[hero5512]

This commit reduces filtermaps memory allocation through two optimizations:

1. Replace map[uint32]struct{} with bitset in matcher
   The indexes in this map are consecutive, so using a bitmap instead of a map can reduce memory allocations.
2. Reuse rowMappingCache across map
   Moved rowMappingCache from local variable to mapRenderer struct field to reuse across renderings instead of creating a new one everytime.

Before optimize:

After optimize:

[rjl493456442]

@zsfelfoldi Please take a look.

Given that the filtermap is under the refactoring, I will let zsolt decide if this change will be suitable in the new code