fix: resolve performance issues

[leg100]

When handling 100s or 1000s of modules some performance issues became evident. This PR fixes those issues.

• prevent concurrent re-building of the explorer tree
• move expensive rendering out of View() into bubbletea cmd
• increase event buffer size to resolve deadlock when handling very large numbers of events (this is a hack and the underlying deadlock should really be detected and removed)

Findings from using pprof:

• lipgloss.JoinVertical is expensive and often better replaced with strings.Join(..., "\n")
• lipgloss.Render is expensive
• regexes are expensive
• pprof is good at determining how much is running as part of the Bubbletea event loop, and how much has been farmed out to Bubbletea commands. The bigger percentage of runtime in the latter, the better.