Fix cumulative value calculation for recursive functions in Table view

[secfree]

Problem

In the Table view, recursive functions (functions that appear multiple times in the same call stack) may display Cumulative (%) values greater than 100%. For example (tested with parca 0.25.0):

Root Cause

When building the table, the code iterates through each frame in a stacktrace and adds the sample value to that function's cumulative. When a function appears multiple times in the same stacktrace (due to recursion), its cumulative value gets counted multiple times.

Example:

Stacktrace: [A → B → A → D], value = 50

Before fix:
  Frame A: cumulative += 50  → 50
  Frame B: cumulative += 50  → 50
  Frame A: cumulative += 50  → 100  // Counted twice!
  Frame D: cumulative += 50  → 50

Function A Cumulative (%) = 100/50 = 200%  // Exceeds 100%

Solution

Track which table rows have been counted for each sample using a seenInSample map. Only add to cumulative for the first occurrence of a function in each sample, while still maintaining caller/callee relationships for all occurrences.

After fix:
  Frame A: first seen, +50     → cumulative = 50
  Frame B: first seen, +50     → cumulative = 50
  Frame A: already seen, SKIP  → cumulative = 50 (unchanged)
  Frame D: first seen, +50     → cumulative = 50

Function A Cumulative (%) = 50/50 = 100% 

[secfree]

@brancz can you help take a look? Thank you.