chore(core): Add directory-watching to 'watcher2'

[timoffex]

Description

Adds WatchDir function to the watcher2 package, making watcher redundant. I will delete watcher after removing references in tb.go.

[codecov]

Codecov Report

Attention: Patch coverage is 63.15789% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 75.79%. Comparing base (5612829) to head (4a74de4).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7596      +/-   ##
==========================================
+ Coverage   75.76%   75.79%   +0.03%     
==========================================
  Files         502      502              
  Lines       54003    54016      +13     
==========================================
+ Hits        40914    40944      +30     
+ Misses      12676    12659      -17     
  Partials      413      413              

Flag	Coverage Δ
func	41.17% <ø> (+0.04%)	⬆️
system	63.35% <20.00%> (-0.02%)	⬇️
unit	56.39% <63.15%> (+0.07%)	⬆️

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Files	Coverage Δ
core/internal/watcher2/impl.go	78.65% <100.00%> (+6.36%)	⬆️
core/internal/watcher2/watcher2.go	100.00% <ø> (ø)
core/internal/watcher2test/watcher2test.go	52.94% <22.22%> (-10.03%)	⬇️

... and 6 files with indirect coverage changes