Add tuple-pattern return, ConnectConfig, and API improvements

[kalidke]

Summary

• BREAKING: frameconnect() now returns (combined, info) tuple instead of NamedTuple
• Add ConnectInfo struct with track assignments and algorithm metadata
• Add ConnectConfig struct for reusable configuration (kwargs also supported)
• Full covariance propagation for SMLMData 0.6 compatibility
• Capture timing with elapsed_s field (Float64 seconds)
• Include counts: n_input, n_tracks, n_combined, n_preclusters
• Rate parameters accessible via info.k_on, info.k_off, etc.
• Bump version to 0.5.0

New API

# Two calling conventions
(combined, info) = frameconnect(smld; maxframegap=10)           # kwargs
(combined, info) = frameconnect(smld, ConnectConfig(maxframegap=10))  # config

# Access results
combined::BasicSMLD           # Main output - combined localizations
info.connected::BasicSMLD     # Input with track_id assigned
info.n_input                  # Number of input localizations
info.n_tracks                 # Number of tracks formed
info.n_combined               # Number of output localizations
info.elapsed_s                # Wall time in seconds
info.k_on, info.k_off         # Estimated rate parameters

ConnectConfig Fields

Field	Default	Description
nnearestclusters	2	Nearest preclusters for local density estimation
nsigmadev	5.0	Sigma multiplier for preclustering distance threshold
maxframegap	5	Maximum frame gap for temporal adjacency
nmaxnn	2	Maximum nearest-neighbors for precluster membership

Test plan

• All 115 tests pass
• Both calling conventions verified equivalent
• Documentation updated (README.md, api_overview.md)

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