Add basic_str_validation cache

[jgkamat]

Currently, this is the most expensive part of string validation, especially on longer strings. Unfortunately, this method is called quite frequently (eg: user agent), during intercept request, and needs to be cheap.

The 'proper' fix for this would be to subclass String (and all other immutable types), add a flag to set when fully validated, and use that flag instead. Ideally, we could do this for dicts too, so we wouldn't need to do the traversal which is extremely costly, and gets even worse if people have bound a lot of keys.

If you'd like, I could try to solve this a different way. This shouldn't take up much more memory because these strings are sitting in the config system anyway, but I really don't like sticking caches on everything instead of the proper fix.

I also made a profile for looking up default bindings 😢 .

Before:

-------------------------------------- benchmark: 4 tests -------------------------------------
Name (time in us)                    Min                    Max                Median          
-----------------------------------------------------------------------------------------------
test_get_str_benchmark[0]         3.6000 (1.0)          12.8400 (1.0)          3.7600 (1.0)    
test_get_str_benchmark[1]        12.8600 (3.57)         31.0200 (2.42)        13.1100 (3.49)   
test_get_str_benchmark[2]       762.0310 (211.68)      982.2980 (76.50)      791.0010 (210.37) 
test_get_dict_benchmark       5,548.5810 (>1000.0)  25,766.7170 (>1000.0)  5,615.2400 (>1000.0)
-----------------------------------------------------------------------------------------------

After

-------------------------------------- benchmark: 4 tests -------------------------------------
Name (time in us)                    Min                    Max                Median          
-----------------------------------------------------------------------------------------------
test_get_str_benchmark[2]         2.8500 (1.0)          25.3700 (2.08)         3.0200 (1.0)    
test_get_str_benchmark[1]         2.9090 (1.02)         23.0900 (1.89)         3.0500 (1.01)   
test_get_str_benchmark[0]         3.0100 (1.06)         12.2000 (1.0)          3.1600 (1.05)   
test_get_dict_benchmark       4,865.0920 (>1000.0)  25,787.3310 (>1000.0)  4,934.3300 (>1000.0)
-----------------------------------------------------------------------------------------------

It's weird that the dict benchmark improved from the string cache, but idk...

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This change is 

[The-Compiler]

Thanks!