Replace pkg_resources file ref with pathlib

[timmysilv]

Context:
FlamingPy started to depend on strawberryfields and importing pkg_resources (by importing this) raises a deprecation warning. Even more concerning, this repo does not express its direct dependency on setuptools despite requiring it (likely because it was shipped with python by default for the longest time).

Description of the Change:
Replace pkg_resources.resource_filename with pathlib.Path(__file__). The data neighbours the source files so pathlib has no problem getting the job done.

Benefits:

• Newer versions of Python do not come with setuptools which makes importing strawberryfields fail
• Other packages (eg. FlamingPy) that depend on strawberryfields can import it without setuptools raising a warning

Possible Drawbacks:
While I'm quite certain that package_data in setup.py doesn't relocate data files, I don't know if there's something in a PEP that says it isn't necessary and some build tools don't respect it.

strawberryfields/setup.py

Lines 45 to 46 in cc0a0e4

	"package_data": {"strawberryfields": ["backends/data/*", "apps/data/feature_data/*",
	"apps/data/sample_data/*"]},

Anyway, installing strawberryfields today does what one would expect:

apps/data/ tree

❯ tree .venv/lib/python3.11/site-packages/strawberryfields/apps/data/
.venv/lib/python3.11/site-packages/strawberryfields/apps/data/
├── __init__.py
├── feature_data
│   ├── MUTAG_exact_fv.npy
│   ├── MUTAG_mat.npy
│   ├── QM9_exact_fv.npy
│   ├── QM9_mat.npy
│   └── QM9_mc_fv.npy
├── feature.py
├── sample_data
│   ├── formic_delta.npz
│   ├── formic_Ud.npz
│   ├── formic_w.npz
│   ├── formic_wp.npz
│   ├── formic.npz
│   ├── MUTAG_0_A.npz
│   ├── MUTAG_0.npz
│   ├── MUTAG_1_A.npz
│   ├── MUTAG_1.npz
│   ├── MUTAG_2_A.npz
│   ├── MUTAG_2.npz
│   ├── MUTAG_3_A.npz
│   ├── MUTAG_3.npz
│   ├── p_hat300-1_A.npz
│   ├── p_hat300-1.npz
│   ├── planted_A.npz
│   ├── planted.npz
│   ├── pyrrole_Lf.npz
│   ├── pyrrole_Li.npz
│   ├── pyrrole_m.npz
│   ├── pyrrole_rf.npz
│   ├── pyrrole_ri.npz
│   ├── pyrrole_U.npz
│   ├── pyrrole_wf.npz
│   ├── pyrrole_wi.npz
│   ├── pyrrole.npz
│   ├── TACE-AS_A.npz
│   ├── TACE-AS.npz
│   ├── water_U.npz
│   ├── water_w.npz
│   └── water.npz
└── sample.py

Related GitHub Issues:
N/A

[codecov]

Codecov Report

Attention: Patch coverage is 27.27273% with 16 lines in your changes missing coverage. Please review.

Project coverage is 60.67%. Comparing base (9a9a352) to head (fd916d0).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
strawberryfields/apps/data/sample.py	21.05%	15 Missing ⚠️
strawberryfields/apps/data/feature.py	66.66%	1 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (9a9a352) and HEAD (fd916d0). Click for more details.

HEAD has 2 uploads less than BASE

Flag	BASE (9a9a352)	HEAD (fd916d0)
	7	5

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #758       +/-   ##
===========================================
- Coverage   98.33%   60.67%   -37.66%     
===========================================
  Files          78       78               
  Lines        9603     9539       -64     
===========================================
- Hits         9443     5788     -3655     
- Misses        160     3751     +3591     

Files with missing lines	Coverage Δ
strawberryfields/apps/data/feature.py	73.33% <66.66%> (-25.03%)	⬇️
strawberryfields/apps/data/sample.py	65.32% <21.05%> (-34.68%)	⬇️

... and 74 files with indirect coverage changes

---

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