feat(neon): Add feature flag for enabling macros

[kjvalencik]

This allows making the linkme dependency optional which may be problematic on some platforms.

We may want to wait for reported problems before we add this complexity. While adding a default feature flag is not considered a breaking change, it can break builds for anyone using default-features = false.

[github-actions]

Bencher Report

Branch	kv/export-flag
Testbed	ubuntu-latest

🚨 1 Alert

Benchmark	Measure Units	View	Benchmark Result (Result Δ%)	Upper Boundary (Limit %)
JsFunction::call	Throughput operations / second (ops/s)	📈 plot 🚷 threshold 🚨 alert (🔔)	5,078,147.36 ops/s (+10.59%) Baseline: 4,591,850.07 ops/s	5,051,035.08 ops/s (100.54%)

Click to view all benchmark results

Benchmark	Latency	Benchmark Result nanoseconds (ns) (Result Δ%)	Lower Boundary nanoseconds (ns) (Limit %)	Upper Boundary nanoseconds (ns) (Limit %)	Throughput	Benchmark Result operations / second (ops/s) (Result Δ%)	Lower Boundary operations / second (ops/s) (Limit %)	Upper Boundary operations / second (ops/s) (Limit %)
JsFunction::bind	📈 view plot 🚷 view threshold	207.96 ns (+0.67%) Baseline: 206.58 ns	185.92 ns (89.40%)	413.15 ns (50.33%)	📈 view plot 🚷 view threshold	4,809,855.49 ops/s (-0.29%) Baseline: 4,823,941.40 ops/s	0.00 ops/s (0.00%)	5,306,335.54 ops/s (90.64%)
JsFunction::call	📈 view plot 🚷 view threshold	196.04 ns (-9.69%) Baseline: 217.08 ns	195.37 ns (99.66%)	434.15 ns (45.15%)	📈 view plot 🚷 view threshold 🚨 view alert (🔔)	5,078,147.36 ops/s (+10.59%) Baseline: 4,591,850.07 ops/s	0.00 ops/s (0.00%)	5,051,035.08 ops/s (100.54%)
JsFunction::call_with	📈 view plot 🚷 view threshold	190.64 ns (-7.27%) Baseline: 205.58 ns	185.02 ns (97.06%)	411.17 ns (46.36%)	📈 view plot 🚷 view threshold	5,247,082.91 ops/s (+8.34%) Baseline: 4,843,299.35 ops/s	0.00 ops/s (0.00%)	5,327,629.29 ops/s (98.49%)
auto-exported-noop	📈 view plot 🚷 view threshold	30.26 ns (-1.07%) Baseline: 30.58 ns	27.52 ns (90.97%)	61.16 ns (49.47%)	📈 view plot 🚷 view threshold	33,218,206.09 ops/s (-0.57%) Baseline: 33,408,575.34 ops/s	0.00 ops/s (0.00%)	36,749,432.87 ops/s (90.39%)
hello-world	📈 view plot 🚷 view threshold	53.16 ns (-6.77%) Baseline: 57.02 ns	51.32 ns (96.54%)	114.04 ns (46.61%)	📈 view plot 🚷 view threshold	18,795,620.18 ops/s (+7.38%) Baseline: 17,503,084.53 ops/s	0.00 ops/s (0.00%)	19,253,392.98 ops/s (97.62%)
manually-exported-noop	📈 view plot 🚷 view threshold	29.91 ns (+4.93%) Baseline: 28.51 ns	25.66 ns (85.77%)	57.01 ns (52.46%)	📈 view plot 🚷 view threshold	33,487,632.03 ops/s (-4.43%) Baseline: 35,038,668.31 ops/s	0.00 ops/s (0.00%)	38,542,535.14 ops/s (86.88%)

🐰 View full continuous benchmarking report in Bencher

[codecov]

Codecov Report

Attention: Patch coverage is 52.94118% with 32 lines in your changes missing coverage. Please review.

Project coverage is 82.77%. Comparing base (2335828) to head (767d22d).

Files with missing lines	Patch %	Lines
crates/neon-macros/src/lib.rs	0.00%	13 Missing ⚠️
crates/neon/src/macro_internal/export.rs	71.42%	10 Missing ⚠️
crates/neon/src/context/internal.rs	55.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1112      +/-   ##
==========================================
- Coverage   82.85%   82.77%   -0.08%     
==========================================
  Files          74       74              
  Lines        4701     4721      +20     
  Branches     4701     4721      +20     
==========================================
+ Hits         3895     3908      +13     
- Misses        713      721       +8     
+ Partials       93       92       -1     

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