fix: support for nested parameters and FuncParam reference

[Miksus]

This PR allows having (session) parameters in other parameters. Might allow recursion.

It also makes it possible to reference the function as the parameter name.

These are now possible:

from rocketry.args import Arg

@app.param("my_arg_1")
def get_arg_1():
    ...

@app.param("my_arg_2")
def get_arg_2(subarg=Arg("my_arg_1")):
    ... # Nested parameter

@app.task()
def do_things(arg_1=Arg("my_arg_1"), arg_2=Arg(get_arg_2)):
    ...

[codecov-commenter]

Codecov Report

Merging #56 (b0c9d59) into master (7599e82) will increase coverage by 0.07%. The diff coverage is 97.29%.

@@            Coverage Diff             @@
##           master      #56      +/-   ##
==========================================
+ Coverage   90.71%   90.79%   +0.07%     
==========================================
  Files          87       87              
  Lines        4038     4050      +12     
==========================================
+ Hits         3663     3677      +14     
+ Misses        375      373       -2     

Impacted Files	Coverage Δ
rocketry/tasks/command.py	91.11% <ø> (+3.87%)	:arrow_up:
rocketry/args/builtin.py	89.87% <95.45%> (-1.80%)	:arrow_down:
rocketry/args/secret.py	77.77% <100.00%> (ø)
rocketry/core/parameters/parameters.py	94.73% <100.00%> (+0.29%)	:arrow_up:
rocketry/core/task.py	92.96% <100.00%> (+0.35%)	:arrow_up:
rocketry/parameters/func.py	100.00% <100.00%> (ø)
rocketry/session.py	91.50% <100.00%> (+0.09%)	:arrow_up:

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