feat: static dispatch for jsonrpc request handlers

[brbrr]

Bench results:

Time (sec/op)

Benchmark	main	native	sonic	native vs main	sonic vs main
no_params	1.638 µs	1.467 µs	1.070 µs	−10.5%	−34.7%
one_scalar_pos	2.431 µs	2.385 µs	1.839 µs	~	−24.3%
one_struct_pos	2.991 µs	2.931 µs	1.963 µs	~	−34.4%
three_pos_mixed	3.774 µs	4.101 µs	2.188 µs	+8.7%	−42.0%
three_named_required	4.045 µs	4.430 µs	2.509 µs	+9.5%	−38.0%
named_opt_missing	2.526 µs	2.762 µs	2.149 µs	+9.3%	−14.9%
named_opt_present	4.016 µs	4.328 µs	2.504 µs	+7.8%	−37.6%
validator_pass	3.003 µs	3.138 µs	2.139 µs	~	−28.8%
validator_fail	3.570 µs	3.905 µs	2.733 µs	+9.4%	−23.4%
type_error	2.446 µs	2.955 µs	3.232 µs	+20.8%	+32.2%
batch_small	15.64 µs	15.71 µs	10.41 µs	~	−33.4%
batch_large	140.9 µs	130.9 µs	82.49 µs	−7.1%	−41.4%
response_100_structs	7.099 µs	6.905 µs	12.19 µs	−2.7%	+71.7%
geomean	4.819 µs	4.975 µs	3.678 µs	+3.2%	−23.7%

Allocs/op

Benchmark	main	native	sonic	native vs main	sonic vs main
no_params	21	19	16	−9.5%	−23.8%
one_scalar_pos	32	35	27	+9.4%	−15.6%
one_struct_pos	43	39	28	−9.3%	−34.9%
three_pos_mixed	56	54	28	−3.6%	−50.0%
three_named_required	55	48	26	−12.7%	−52.7%
named_opt_missing	33	33	25	~	−24.2%
named_opt_present	55	48	26	−12.7%	−52.7%
validator_pass	42	40	29	−4.8%	−31.0%
validator_fail	54	53	42	−1.9%	−22.2%
type_error	35	39	43	+11.4%	+22.9%
batch_small	131	121	107	−7.6%	−18.3%
batch_large	997	897	788	−10.0%	−21.0%
response_100_structs	21	20	17	−4.8%	−19.1%
geomean	54.24	51.75	38.65	−4.6%	−28.7%

Bytes/op

Benchmark	main	native	sonic	native vs main	sonic vs main
no_params	1.617 KiB	1.578 KiB	1.272 KiB	−2.4%	−21.3%
one_scalar_pos	1.892 KiB	2.759 KiB	2.512 KiB	+45.8%	+32.8%
one_struct_pos	2.501 KiB	2.899 KiB	2.675 KiB	+15.9%	+7.0%
three_pos_mixed	3.017 KiB	3.447 KiB	2.777 KiB	+14.3%	−7.9%
three_named_required	3.221 KiB	2.978 KiB	3.226 KiB	−7.6%	~
named_opt_missing	2.259 KiB	2.392 KiB	2.929 KiB	+5.9%	+29.7%
named_opt_present	3.229 KiB	2.985 KiB	3.212 KiB	−7.5%	~
validator_pass	2.440 KiB	2.848 KiB	2.580 KiB	+16.7%	+5.7%
validator_fail	3.180 KiB	3.603 KiB	3.656 KiB	+13.3%	+15.0%
type_error	2.221 KiB	3.072 KiB	3.927 KiB	+38.4%	+76.9%
batch_small	11.06 KiB	10.86 KiB	10.62 KiB	−1.8%	−4.0%
batch_large	87.09 KiB	85.13 KiB	89.83 KiB	−2.3%	+3.2%
response_100_structs	4.213 KiB	4.181 KiB	5.015 KiB	−0.8%	+19.0%
geomean	3.828 KiB	4.163 KiB	4.203 KiB	+8.8%	+9.8%

The typed-dispatch refactor only eliminates reflection in the handler call (replacing reflect.Value.Call with a typed closure), but per-request time is dominated by encoding/json's
reflection-driven decode of params — which we still pay because we still use stdlib JSON. The call-site reflection we removed costs ~30-50ns; the per-field json.Unmarshal reflect walks
we kept cost ~400ns each, so the savings get drowned out. The only paths that visibly benefit are call-overhead-dominated ones (no-args, batches, encode-heavy) where the reflect.Call
savings aren't masked — decode-heavy paths come out at parity with main.

[codecov]

Codecov Report

❌ Patch coverage is 41.60959% with 341 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.96%. Comparing base (13295a2) to head (c10229d).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
rpc/v10/register.go	2.75%	105 Missing and 1 partial ⚠️
rpc/v8/register.go	11.32%	93 Missing and 1 partial ⚠️
rpc/v9/register.go	13.76%	93 Missing and 1 partial ⚠️
jsonrpc/server.go	59.61%	15 Missing and 6 partials ⚠️
jsonrpc/register.go	89.07%	10 Missing and 10 partials ⚠️
rpc/handlers.go	76.92%	0 Missing and 3 partials ⚠️
rpc/v8/subscriptions.go	60.00%	2 Missing ⚠️
rpc/v9/subscriptions.go	75.00%	1 Missing ⚠️

❌ Your patch check has failed because the patch coverage (41.60%) is below the target coverage (60.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3649      +/-   ##
==========================================
- Coverage   77.12%   71.96%   -5.17%     
==========================================
  Files         395      399       +4     
  Lines       35645    36602     +957     
==========================================
- Hits        27492    26340    -1152     
- Misses       6153     8139    +1986     
- Partials     2000     2123     +123     

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