trx_toolkit/*: Represent bursts as arrays instead of lists

Continuing fake_trx profiling story I noticed that on rx path a
noticeable time is spent in converting from ubits to sbits via list
comprehensions. By changing burst representation from py list, which
stores each item as full python object, to an array, which stores each
item as just byte, and by leveraging bytearray.translate, we can speed
up that conversion by ~ 10x:

before:

    In [1]: from data_msg import Msg

    In [2]: burst = [0, 1] * (142//2)

    In [3]: burst
    Out[3]:
    [0,
     1,
     0,
     1,
     0,
     ...
     0,
     1]

    In [4]: Msg.ubit2sbit(burst)
    Out[4]:
    [127,
     -127,
     127,
     -127,
     ...
     127,
     -127]

    In [5]: %timeit Msg.ubit2sbit(burst)
    3.01 µs ± 43.3 ns per loop (mean ± std. dev. of 7 runs, 100,000 loops each)

after:

    In [2]: burst = bytearray([0, 1] * (142//2))

    In [3]: burst
    Out[3]: bytearray(b'\x00\x01\x00\x01...\x00\x01')

    In [4]: Msg.ubit2sbit(burst)
    Out[4]: array('b', [127, -127, 127, -127, ... 127, -127])

    In [5]: %timeit Msg.ubit2sbit(burst)
    325 ns ± 12.1 ns per loop (mean ± std. dev. of 7 runs, 1,000,000 loops each)

Change-Id: I7314e9e79752e06fa86b9e346a9beacc5e59579e
---
M src/target/trx_toolkit/data_msg.py
M src/target/trx_toolkit/gsm_shared.py
M src/target/trx_toolkit/rand_burst_gen.py
M src/target/trx_toolkit/test_data_msg.py
4 files changed, 36 insertions(+), 25 deletions(-)