`trace.CoverageResults.__init__` does not copy the counts dict

Issue

CoverageResults.__init__ copies calledfuncs and callers via .copy() but assigns counts directly. This means self.counts is an alias to the caller's dict, and calling update() mutates the original dict passed to the constructor.

Reproducer

from trace import CoverageResults

# counts is NOT copied — original is mutated:
counts = {}
cr = CoverageResults(counts=counts)
cr.update(CoverageResults(counts={('file.py', 1): 5}))
print(counts)  # {('file.py', 1): 5} — mutated

# calledfuncs IS copied — original is not mutated:
calledfuncs = {}
cr = CoverageResults(calledfuncs=calledfuncs)
cr.update(CoverageResults(calledfuncs={('file.py', 'mod', 'func'): 1}))
print(calledfuncs)  # {} — not mutated

Impact

The documentation states that CoverageResults "should not be created directly by the user," so direct external impact is limited. However, the inconsistency also affects internal usage: Trace.results() passes its internal self.counts directly to the constructor, so calling update() on the returned CoverageResults will mutate the Trace object's internal state.

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-146176
• gh-146183

Start in Lib/trace.py at CoverageResults.init and Trace.results(), where the issue says the counts dictionary is passed through. Check the existing update behavior and add coverage for preserving the caller's dictionary; done means updating a CoverageResults no longer mutates the dictionary supplied by the constructor or the Trace object's internal state.