feat: set default Rust toolchain

[eduardoboucas]

- Summary

Before installing the Rust build target, sets the default toolchain to stable via the rustup default command. Because this is the one with less precedence out of all the override methods, users still have the option to specify a different toolchain using any of the other four methods.

- Test plan

Adjusted existing test.

- A picture of a cute animal (not mandatory but encouraged)

[github-actions]

⏱ Benchmark results

Comparing with 67961ee

largeDepsEsbuild: 12.9s

⬇️ 0.73% decrease vs. 67961ee

^                          14.6s                                                                          
│                           ┌──┐                                                                          
│          13.1s            |  |           12.9s                                                   12.9s  
│           ┌──┐            |  |   12.8s    ┌──┐           12.5s   12.8s                   12.6s    ┌──┐  
│ ──────────┼──┼────────────┼──┼────┌──┐────┼──┼───11.6s────┌──┐────┌──┐───11.7s────────────┌──┐────|▒▒|──
│  10.9s    |  |            |  |    |  |    |  |    ┌──┐    |  |    |  |    ┌──┐   11.1s    |  |    |▒▒|  
│   ┌──┐    |  |   10.4s    |  |    |  |    |  |    |  |    |  |    |  |    |  |    ┌──┐    |  |    |▒▒|  
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└───┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴──>
    T-12    T-11    T-10    T-9     T-8     T-7     T-6     T-5     T-4     T-3     T-2     T-1      T    

Legend

• T-14 (67961ee): 13s
• T-13 (413e5dc): 13.7s
• T-12 (4bbd835): 10.9s
• T-11 (13f7579): 13.1s
• T-10 (2139bea): 10.4s
• T-9 (920c5bc): 14.6s
• T-8 (2fbb403): 12.8s
• T-7 (5078244): 12.9s
• T-6 (1e3ac5a): 11.6s
• T-5 (9eb9ea6): 12.5s
• T-4 (b2bf035): 12.8s
• T-3 (55b5529): 11.7s
• T-2 (9442aaf): 11.1s
• T-1 (e38f0a0): 12.6s
• T (current commit): 12.9s

largeDepsZisi: 1m 11.7s

⬇️ 2.48% decrease vs. 67961ee

^                         1m 22.8s                                                                        
│                           ┌──┐                                                                          
│                           |  |                                                                          
│         1m 11.5s          |  |  1m 10.7s1m 10.2s                                                1m 11.7s
│           ┌──┐            |  |    ┌──┐    ┌──┐          1m 4.9s 1m 7.5s                 1m 7.7s   ┌──┐  
│ ──────────┼──┼────────────┼──┼────┼──┼────┼──┼────────────┌──┐────┌──┐────────────────────┌──┐────|▒▒|──
│  58.2s    |  |   55.9s    |  |    |  |    |  |   57.8s    |  |    |  |   59.5s    59s     |  |    |▒▒|  
│   ┌──┐    |  |    ┌──┐    |  |    |  |    |  |    ┌──┐    |  |    |  |    ┌──┐    ┌──┐    |  |    |▒▒|  
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│   |  |    |  |    |  |    |  |    |  |    |  |    |  |    |  |    |  |    |  |    |  |    |  |    |▒▒|  
└───┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴──>
    T-12    T-11    T-10    T-9     T-8     T-7     T-6     T-5     T-4     T-3     T-2     T-1      T    

Legend

• T-14 (67961ee): 1m 13.5s
• T-13 (413e5dc): 1m 12.8s
• T-12 (4bbd835): 58.2s
• T-11 (13f7579): 1m 11.5s
• T-10 (2139bea): 55.9s
• T-9 (920c5bc): 1m 22.8s
• T-8 (2fbb403): 1m 10.7s
• T-7 (5078244): 1m 10.2s
• T-6 (1e3ac5a): 57.8s
• T-5 (9eb9ea6): 1m 4.9s
• T-4 (b2bf035): 1m 7.5s
• T-3 (55b5529): 59.5s
• T-2 (9442aaf): 59s
• T-1 (e38f0a0): 1m 7.7s
• T (current commit): 1m 11.7s