Remove several functions and objects from PyMC root namespace

[ricardoV94]

• [x] All arviz plots must be retrieved from pymc.plots.foo
• [x] All arviz stats must be retrieved from pymc.stats.foo
• [x] Removed many rare or non-user facing objects
• [ ] Remove rare or non-user facing VI objects (I am not familiar enough to know which ones should stay and which ones should not)

Closes #6761

Also

• [x] Move all custom Exceptions to pymc.exceptions.py

The following script prints 174 after and 272 before this PR:

import pymc
from types import ModuleType
len([a for a in dir(pymc) if not isinstance(getattr(pymc, a), ModuleType) and not a.startswith("__")])

The following entries were removed:

CallableTensor
DictToArrayBijection
ELPDData
GeneratorAdapter
ImputationWarning
IncorrectArgumentsError
SamplingError
ShapeError
ShapeWarning
TraceDirectoryError
_calculate_ics
apply_test_function
autocorr
autocorrplot
autocov
bfmi
bool_types
compare
compareplot
complex_types
compute_log_likelihood
cont_inputs
continuous_types
convert_observed_data
densityplot
discrete_types
drop_warning_stat
energyplot
ess
expand_packed_triangular
float_types
forestplot
generator
guess_scaling
hdi
int_types
invlogit
invprobit
isgenerator
join_nonshared_inputs
kde
kdeplot
logaddexp
logit
logsumexp
loo
loo_pit
make_shared_replacements
make_ufunc
mcse
pairplot
plot_autocorr
plot_bf
plot_bpv
plot_compare
plot_density
plot_dist
plot_dist_comparison
plot_dot
plot_ecdf
plot_elpd
plot_energy
plot_ess
plot_forest
plot_hdi
plot_kde
plot_khat
plot_lm
plot_loo_pit
plot_mcse
plot_pair
plot_parallel
plot_posterior
plot_ppc
plot_rank
plot_separation
plot_trace
plot_ts
plot_violin
predictions_to_inference_data
probit
psislw
r2_samples
r2_score
reloo
rhat
smartfloatX
str_for_dist
str_for_model
str_for_potential_or_deterministic
summary
to_inference_data
trace_cov
traceplot
typefilter
waic
weight_predictions
wrap_xarray_ufunc

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:books: Documentation preview :books:: https://pymc--6973.org.readthedocs.build/en/6973/