perf(Signal): speed up multicast dispatch; chore: normalise line endings to LF

[glennawatson]

Two independent changes (squash-merge will keep them as one; the commits are atomic if you prefer rebase):

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perf(Signal): typed observer/action fields for multicast dispatch

Signal<T>.SignalSubscription stored its target in a single object _target and, on every dispatched callback, did an is Action<T> type-test plus an (IObserver<T>)_target cast. On the multicast hot path (DispatchSubscriptions) that isinst+castclass runs once per observer per value.

This switches the subscription to two typed fields — IObserver<T>? _observer and Action<T>? _action — so dispatch branches on a cheap null check. OnError/OnCompleted collapse to _observer?.On…(…). The single-observer/single-action fast paths are unchanged.

Results

ShortRun, net10.0, 1024 emits fanned out to N observers (new SubjectMulticastBenchmarks):

Signal multicast (1024 emits)	Before	After	System.Reactive	R3
×4 observers	6.98 µs	5.76 µs (−17.5%)	5.25 µs	8.71 µs
×8 observers	12.11 µs	10.52 µs (−13.2%)	9.88 µs	17.0 µs

Signal<T> goes from ~24–28% behind System.Reactive.Subject<T> to ~6–9%, stays well ahead of R3, and keeps the lowest allocation of the three. Cost is +8 bytes per SignalSubscription (one extra reference field).

All 221 ReactiveUI.Primitives.Tests pass (net9.0); behaviour preserved (action subscriptions still ignore OnError/OnCompleted, now via the null _observer).

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chore: normalise line endings to LF

.gitattributes forced eol=crlf on checkout while storing LF blobs, and even marked *.sh eol=crlf (which corrupts shell scripts). Switched the global rule to plain * text=auto and dropped the forced eol=crlf from *.sln, *.sh, *.cmd, *.bat, so working trees check out LF on every platform.

git add --renormalize . confirmed every blob was already LF, so the only committed change is .gitattributes itself.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.56%. Comparing base (d8c6eda) to head (4decf60).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #17      +/-   ##
==========================================
+ Coverage   91.53%   91.56%   +0.02%     
==========================================
  Files         398      399       +1     
  Lines       15481    15546      +65     
  Branches     2231     2248      +17     
==========================================
+ Hits        14171    14235      +64     
+ Misses        990      989       -1     
- Partials      320      322       +2     

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