Add Symbolic number constructor and conversion

[bowenszhu]

• fix Simplifying construstion of symbolic numbers Symbolics.jl#853
• fix Casts from float64, int64, to symbolic types are missing #601

This pull request adds a constructor and a conversion function for Symbolic objects representing numbers.

Key changes:

• Symbolic constructor:

  • The Symbolic(x::T) where {T<:Number} constructor now creates a Term object from a number x, inferring the type of the Symbolic object from the type of x.
  • The Symbolic{T}(x::Number) where {T} constructor now creates a Term object with the specified type T, converting x to that type if necessary.

• convert function:

  • The convert(::Type{<:Symbolic{T}}, x::Number) where {T} function now converts a number x to a Term object of the specified type T.

• Tests:

  • The test suite now includes tests for the Symbolic constructor and convert function, ensuring correct behavior for various numeric types, including Int, Float64, Rational, and Complex.
  • The test suite also includes a test case demonstrating how the convert function works when assigning a number to an array of Symbolic.

These changes provide a more convenient and flexible way to create and work with symbolic representations of numbers, and hide the internal Symbolic subtype system from external users.

[github-actions]

Benchmark Results

	master	dfec04e...	master/dfec04ec7c5196...
overhead/acrule/a+2	0.713 ± 0.016 μs	0.735 ± 0.017 μs	0.97
overhead/acrule/a+2+b	0.691 ± 0.015 μs	0.71 ± 0.018 μs	0.974
overhead/acrule/a+b	0.26 ± 0.0091 μs	0.255 ± 0.013 μs	1.02
overhead/acrule/noop:Int	25.9 ± 0.059 ns	24.7 ± 0.92 ns	1.05
overhead/acrule/noop:Sym	0.0363 ± 0.0056 μs	0.0421 ± 0.006 μs	0.863
overhead/rule/noop:Int	0.044 ± 0.0012 μs	0.0438 ± 0.0014 μs	1
overhead/rule/noop:Sym	0.0546 ± 0.0024 μs	0.0542 ± 0.0022 μs	1.01
overhead/rule/noop:Term	0.0544 ± 0.0024 μs	0.0545 ± 0.0016 μs	0.997
overhead/ruleset/noop:Int	0.132 ± 0.0037 μs	0.132 ± 0.0045 μs	0.999
overhead/ruleset/noop:Sym	0.155 ± 0.0051 μs	0.154 ± 0.0033 μs	1.01
overhead/ruleset/noop:Term	3.8 ± 0.14 μs	3.77 ± 0.14 μs	1.01
overhead/simplify/noop:Int	0.141 ± 0.0031 μs	0.138 ± 0.0031 μs	1.02
overhead/simplify/noop:Sym	0.154 ± 0.0029 μs	0.152 ± 0.0025 μs	1.01
overhead/simplify/noop:Term	0.038 ± 0.0019 ms	0.0377 ± 0.0023 ms	1.01
overhead/simplify/randterm (+, *):serial	0.117 ± 0.0034 s	0.119 ± 0.004 s	0.985
overhead/simplify/randterm (+, *):thread	0.0723 ± 0.021 s	0.0741 ± 0.024 s	0.975
overhead/simplify/randterm (/, *):serial	0.221 ± 0.005 ms	0.223 ± 0.0061 ms	0.987
overhead/simplify/randterm (/, *):thread	0.252 ± 0.0056 ms	0.252 ± 0.0069 ms	1
overhead/substitute/a	0.0609 ± 0.0014 ms	0.0603 ± 0.0014 ms	1.01
overhead/substitute/a,b	0.0534 ± 0.0014 ms	0.052 ± 0.0013 ms	1.03
overhead/substitute/a,b,c	17.5 ± 0.57 μs	16.3 ± 0.61 μs	1.07
polyform/easy_iszero	0.0337 ± 0.0016 ms	0.0341 ± 0.0017 ms	0.989
polyform/isone	3.1 ± 0.01 ns	2.79 ± 0.01 ns	1.11
polyform/iszero	1.79 ± 0.03 ms	1.8 ± 0.032 ms	0.993
polyform/simplify_fractions	2.41 ± 0.038 ms	2.4 ± 0.04 ms	1
time_to_load	4.52 ± 0.014 s	4.53 ± 0.029 s	0.999

Benchmark Plots

A plot of the benchmark results have been uploaded as an artifact to the workflow run for this PR.
Go to "Actions"->"Benchmark a pull request"->[the most recent run]->"Artifacts" (at the bottom).

[bowenszhu]

I'm closing this pull request because we've decided to implement the feature using a different approach that will be more efficient and scalable. I'll create a new pull request for this alternative solution soon.

• Add Const(::Any) to make BasicSymbolic fully closed #612